"Since" has multiple meanings and uses in English:

1. **Temporal Meaning**: When used as a conjunction, "since" indicates a point in time or a duration starting from a specific time in the past up to the present. For example:
- "I have been living here since 2010." (Duration)
- "I haven't seen her since yesterday." (Point in time)

2. **Causal Meaning**: It can also indicate a reason or cause, often used at the beginning of a sentence. For example:
- "Since it's raining, we should stay indoors." (Reason)

3. **Adverbial Meaning**: As an adverb, "since" can mean "from then until now." For example:
- "She left an hour ago and hasn't returned since."

The usage of "since" depends on the context of the sentence and the intended meaning.