I use this word in my daily language even without knowing what it actually means.
Technically speaking, there is no big difference between […] and […].
(1) I like the Wiktionary definition which is "based on precise facts". Consider the following example:
I earn $9,000 per year and live comfortably, although technically I am below the poverty line.
"Technically" is used to introduce the contrasting observation that although the author considers herself well-off, she is in fact a pauper based on a precise definition of poverty. This use of "technically" to provide contrast seems typical.
I would not agree that "technically" and "literally" are interchangeable. "Literally" refers to the literal as opposed to figurative meaning of a word or phrase.
(2) Many words and phrases originate in technical jargon, where they had meanings specific to the relevant field; later, they are often popularized in regular language, where their meaning changes into something more general, less specific to the field. We may then say that such an expression is used either technically/narrowly/strictly or broadly/generally/popularly.
Kate Moss is really obese: Chanel won't hire her any more. I mean, she isn't technically obese, since her Body Mass Index, the number doctors use to determine obesity, is still quite low; but that doesn't matter on the catwalk.
Since technical jargon is often more precise and detailed than other language, the phrase technically [speaking] is tending to develop a meaning identical to strictly speaking, as in your example. This in turn may sometimes even evolve into something closer to a general intensifier, like really.
This broader use of technically is resisted by some, who feel that it introduces another synonym of strictly that we hardly need, while rendering its original sense, as used in the relevant field, unusable. They advise that technically be reserved for expressions used in a sense specific to a certain field or profession, as opposed to cases where strictly would do. ( ... ... )
(3) If you describe something as technical, you're suggesting there are many detailed aspects and implying that perhaps it isn't reasonable to go into so much depth. So following this logic, technically is stating that something, as a result of many detailed aspects, would shed light in a different manner, usually contrary to what has been said previously as if to demonstrate a point.
In other words, you could replace technically with "If we went into more detail, you'd find that the following is true..."
(1) Well it has many meanings. At some situations it might be synonym for for example "precisely speaking" but in those situations to[?the] person usually tells the extra details immediately saying that.
But usually using technically speaking means that there's some duality of doubt...usually some ugly surprise that people try to avoid telling...and say "technically" in some kind of way of being semi-honest. They give you to chance to ask what he/she means by that "technically" part but if you don't ask he/she can always shrug off their responsibility for not telling by saying that you get the chance to ask because they said "technically". It's like those special clauses printed in small font in agreement papers.
"Technically single" could have tens of different meanings for example:
1) the person is still married but has just filed for divorce
2) the persons partner is working late today! Perfect time to cheat! But then the poor bastard decides to come home early....
3) the persons partner works in other continent...so there's almost minuscule chances of him/her caught his/her spouse cheating
4) the person has psychopathic overjealous ex- who hunts down his/her every new date. In that case "technically" is warning.
Generally "technically" speaking is sign of conflicting/contradicting facts. Person could be member of some religious community as matter of habit but in reality he wouldn't believe into tenets of that faith. So technically he would be for example Christian even if he wouldn't believe to God because state papers say so.
People using "technically" speaking many times gives kinda untrustworthy picture of themselves. For example if some person would say that he's technically American the first thing coming to my mind would be that he would be illegal immigrant and that IRS goons would burst in soon. FREEZE! THIS IS IRS!
(2) Concerning the first response, examples 1-3 are incorrect, at least according to American English usage.
"Technically" implies that based on laws, generally accepted agreements or standards, etc. that someone is in a certain condition.
For the "technically single" examples, only #4 is correct. This person is "technically" single; however, since a crazy ex is stalking here and possibly stopping her from dating other people, it is like she is still in a relationship. An opposite phrase for "technically" is "for all intents and purposes"
In example 3 given above, this person is technically married. According to the laws of his or her nation, he or she is legally bound to the spouse. However, since the spouse is overseas, this person is "for all intents and purposes" single.
Like I stated above, I can only speak for American English though.
(3) When a person says “technically” before their answer, it shows that they are answering the question factually, but they are not answering the real meaning of the question.
For your example… “single” and “married” are opposites. You are either one or the other. If a person asks “Are you single?” the factual question is “are you single or married?” but the real meaning of the question is “are you available for me to date you?” So the answer “technically, I am single” means that I am not married, but there are things that would make me unavailable to date you. I may already have a boyfriend but we’re not married yet or I may be a lesbian and not interested in dating a man, or my husband might have died and I’m single again but not interested in starting over, etc.
-- “Did they offer you the job?”
-- “Technically, no. But they said I should look for a letter from them on Monday.” (This suggests they will offer the job on Monday, but they haven’t offered it yet.)
-- “This house is expensive. Do you have money in the bank for it?”
-- “Technically, no. But I could sell some stocks.” (The money is not in the bank, but I do have money somewhere else, like in investments.)
-- “What a cute photo. Is that your daughter?”
-- “Technically, yes, but I gave her up for adoption right after the photo was taken” (She is biologically my daughter, but I am not the mother who raised her.)