Time series: What is a "non-zero mean"?

Question

I am looking through a few related posts on the topic and often landed in medias res. Therefore, please allow me to ask three directly related questions on time series:

1. What is a time series with a "non-zero mean"?
2. Does it mean that it has an "intercept", or also named "constant"?
3. When a time series has a "trend", does it just mean that it trends up or downwards?

I considered this post here but couldn't fully answer my questions from the example.

Thank you!

Answer 1

1) Any time series which have a non zero mean i.e it follows (mu,sigma-square) distribution

Are we talking about stationarity anywhere

2) A time series intercept can be calcualated based on:

This is the formula

3) If a time series has only trend, then it either decreases or increases, bu tit rarely happens that way, as a time series is generally a mixture of many components like trend, seasonal, cyclical and error component.

A combination of these