The description in the question — a system that temporarily holds and actively processes information to carry out complex cognitive tasks such as language comprehension, learning and reasoning, and that corresponds to whatever you are focusing on right now — is the textbook definition of working memory.

Working memory is the active mental workspace. It does two things at once: it holds a small amount of information briefly and it manipulates that information (comparing, combining, reasoning) to complete demanding tasks. When you follow a spoken sentence, solve a problem mentally, or keep a phone number in mind while dialling, you are using working memory. The phrase "the information you are focusing on at a given moment" points directly to this active, attention-linked processing.

Short-term memory is often confused with working memory, but it refers only to the passive, brief storage of information — holding items without the active manipulation that defines working memory; it is a component within, not equivalent to, the working-memory system. Episodic memory is a long-term store of personally experienced events tied to a specific time and place, not a moment-to-moment processing space. Semantic memory is the long-term store of general facts, concepts and word meanings; it holds knowledge but does not perform the live processing described in the question.

Correct answer: Working memory