My sense is that there's three things going ... maybe four in fact.
Definitions of common words
Asking us to define or make sense of common words is off-topic here. That's for English.SE or ELL.SE or other language SEs accordingly.
Definitions of words that have a common meaning in contemporary philosophy
Some words like "validity", "truth table" from logic and some words like "thing-in-itself", "epoche", "utilitarianism", "Geist" and others have a specific definition in philosophy that is common across multiple philosophers or eras or are idiosyncratic to one philosopher that they have an agreed to definition (in the general contours) among philosophers.
Definitions of words in the vocabulary of a single philosophy
Some words are used in specific ways by individual philosophers and thus on-topic when properly marked. For instance, "metaphysics" and "ontology" are too big to be simply defined for everyone, but if you said "What does Heidegger mean by metaphysics?" or "What is essence in Aristotle?" then the question which would have been too broad for the "common meaning in contemporary philosophy" category becomes sufficiently narrow.
In a sense, the words that are so idiosyncratic to be recognizable "manifold of apperception" are words that shift automatically from the second category to the third category.
The fourth dimension here is that philosophers know (at least within their sub-fields) which words are which.
Functionally for answers, the key is to be able to explain where that philosophers explains or what that philosopher uses the term as for (3). For (2), much of it as so foundational that it's odd to meet someone in philosophy with a substantially different definition (and usually then they know the common definition but don't like it for some reason).