Google gives me 7 million hits for that term, I give you that. However, I suspect most of these hits will be girls getting their pussy licked, not sucking some guys dick. If you use "blowjob" for every kind of oral sex, it makes the tag less useful because it carries less specific information.
Try the very first video, it's quite good
The goal of the whole tagging system is to provide information on the images in form of keywords. Yes, this is about language. If we choose to use terms with several meanings, it becomes unclear what the image actually shows.
We just have "blowjob" tag, without give/get.
Let me answer you with an equally ridiculous statement: We don't need detail. Lets just label every image with sexual content with the tag "sex" and we only need one tag! Great, right?
It only sounds ridiculous from the perspective of the tagging system you wrote, otherwise, plenty of good games can be found that did just that and were really advanced logically otherwise. (what I mean to say is that it is possible to work with a LOT of tags and possible to work with 1), point is to find the acceptable middleground.
Now let's stop playing dumb for a moment and think: The more detailed the description of the image gets, the more tags we will need for it, that is obvious. If you want to make the argument that +- sex tags are too much detail for PyTFall, that's fine. Don't pretend I want to use thousands of tags to describe the images just so you can tell me that is not practical. I know that already and you know that I know 
I've been thinking about it and came to conclusion that creating a system that would search for what you need from to many tags, is almost impossible as a number of tags will always be missing and you are bound to end up getting odd pictures. This can be mitigated somewhat by using "main categories" that will be checked primarily during the sorting.
Otherwise, a decent solution: create a number of unique tags for more/most demanding jobs and events and use that instead of trying to match tags to event content (texts, locations etc.). Will not be universal, but will work really well I expect.
However, I also know that descriptions of group sex scenes (starting with threesomes) are very hard without +- sex tags. Even with them, they are hard, so I've been thinking about alternate solutions - unsuccessfully, so far.
You're right... close to impossible without going overboard with tag descriptors and making images almost impossible to call as required. I think any attempt to describe these without the pinpoint tags for events will be either be to complicated for many modders to understand or will mean a very large leap towards the "thousands tags".
Come on...
Nobody is talking about animation. I am telling you that you will get the same tags for images with different contents. Consider this, using your active/passive approach:
Image 1: Belldandy licks the pussy of another girl, while that girl fingers Belldandys pussy --> "lick pussy", "finger pussy", "active", "passive"
Image 2: Belldandy fingers the pussy of another girl, while that girl licks Belldandys pussy --> "lick pussy", "finger pussy", "active", "passive"
Sorry, I misunderstood what you've meant by passive and active. I though active meant that the main character of the event is taking an active part in an act and passive that she's not (as in being totally receptive in the nature of the event).
Like you've said in the above statement and I said when I requested customizable tooltips, it's important to know what tags actually mean to the game.
IMHO: I think we need to agree on describing either what's been done to MC of the event or what she's doing. If we use both, we'll require separate tags for every participant (prolly an overkill) and I don't see another solution.
From perspective of what's being done to the MC (active/passive means if she's active in the scene like giving a helping hand or doing something other than receiving the "punishment")
Im_1: Should be: "lesbian", "finger pussy" <-- if we have the tag (we prolly should), "active" + other relevant tags
Im_2: Should be: "lesbian", "lick pussy", "active" + other relevant tags
