The best definition for a “geek” is that applied by a court to another hard to define term:

Q: What Is a Geek? A: You know one when you see one.

More specifically, the following may be considered characteric of geeks:

1. Geeks dream not necessarily impossible dreams, but dreams beyond the mainstream. The accolades and reward a geek strives for, and which actually satisfy a geek, are not necessarily bizarre, but are outside the given standard mainstream reward system.

2. There is an interest in technology, not necssarily in the conventional established technology of the time, but in technology as a systematic method of imposing order, even order in areas which may be viewed as peripheral to others.

3. The knowledge is not simply abstract or academic, but is applied to specific situations, whether they are real world applications, or non-existent fantasy worlds which comply with the essential requirement of a fantasy world – that it operate in accordance with a set of consistent rules (the rules may of course, allow inconsistency – as even quantum physics does – but must consistently include inconsistency).. Even if these rules allow inconsistency (quantum physics’s does!)

4. The activity related to the area of interest extends beyond a mere ‘passing interest’ or ‘passtime’, and extends to what might a non-sympathetic observer might term or consider to be “obsessive”.

Busting some canards:

While there has been a tendency to associate ‘geekiness‘ with specific areas of technology – most recently with computer technology – ‘geekiness’ is a moving target. The cycle for successful technologies is that they are introduced, developed, and then become mainstream. Geeks, by virtue of their characteristics, may be early adopters of specific technologies, but the technology did not creat the geek. (Geeks may have created computers. But the discovery of computers did not create geeks.)
There has also been a tendency to equate ‘geeks’ with social ineptitude. While interests outside the mainstream, and an obsessive degree of interest, may be qualities that intersect with individuals who display social ineptitude, social ineptitude in and of itself is not a sine qua non for geekiness, and geeks are not necessarily socially inept.
If your husband is a geek and you have no idea how to surprise him for your anniversary, you may find some ideas at anniversarygiftsforhusband.com. Remember that geeks are humans too and they deserve your love and attention.