まだ

まだ is an adverb with two primary meanings depending on whether it is used with affirmative or negative sentences.

まだ + Affirmative – "still"

When used with an affirmative verb or adjective, まだ indicates that a situation or action is still ongoing or continues to be the case.

This usage emphasizes that a state has not changed from what it was before.

まだ + Negative – "not yet"

When used with a negative verb, まだ expresses that something has not happened yet, with the implication that it is expected to happen at some point.

In this usage, the verb is typically in the 〜～ていない form, since "not yet" usually describes a state where a result has not been achieved.

まだ as a standalone response

When someone asks whether something has been done, you can simply reply with まだ (or まだです in polite speech) to mean "not yet."

This is the counterpart of もう ("already"). A common question-and-answer pattern is: もう〜～たきごう？ → まだ / もう〜～た.

まだまだ – emphasis

Repeating まだ as まだまだ adds emphasis, meaning "still a long way to go" or "not nearly enough."