Is serial correlation and auto correlation the same?

Serial correlation: When regression errors are correlated across observations.

Auto correlation: When a time series is correlated with its own past values.

Seems the definitions are a bit different, but are these things exactly the same?

And what kind of serial correlation can we have, except positive serial correlation?

I would trust wikipedia : Autocorrelation From Wikipedia, the free encyclopedia Autocorrelation , also known as serial correlation (or cross-autocorrelation) Note that negative serial correlation , although rare, is possible

They are the same.