In the context of investing, the terms "stocks" and "shares" have a similar meaning, and are often used interchangeably, particularly in American English.
The difference is that "stocks" appear to be a more general term referring to the piece of ownership in a company or several companies. On the other hand, "shares" mean the same thing, but it is mostly used to describe ownership in a particular company.
For example:
- I invest in stocks.
- I invest in Apple shares.
While these terms can be used as synonyms in a standard description of financial markets, be aware that they have more distinctive meanings in some countries and languages.