A share is one unit; stock is the general holding made up of those units. So you say "she owns a hundred shares" but "he has stock in the company" — think of stock as the whole pie and a share as one slice of it.
The core difference
Stock refers to ownership in a company in general terms, while a share is a single, countable unit of that ownership.
- stock — a holding of partial ownership in a company, spoken of as an uncountable whole: He bought stock in a tech company last year.
- share — one countable unit of ownership in a company: She bought a hundred shares in the technology company.
How to tell them apart
The quickest test is counting. You can count shares — one share, a hundred shares — but you cannot count "stocks" the same way when talking about a single company; instead people say someone "holds stock" or "owns stock" as a general position. Financial reports and brokers often use the words loosely and interchangeably outside this strict distinction, which is where most of the confusion comes from.
Away from finance, the two words split further: stock can also mean a shop's goods for sale or a cooking liquid, while share keeps its everyday sense of a portion divided among people, such as a share of a bill.
