In my opinion it happens too often that these important web analytics terms get mixed up or misunderstood. Sometimes even people that work in the internet industry seem to get confused. Whenever you have doubts if your conversation partner understood these terms right, you should better explain these differences again! See below the official definitions, where i have marked the parts with [!] that are in my experience most often misunderstood.
The official definitions according to Google:
A pageview is defined as a view of a page on your site that is being tracked by the Analytics tracking code. If a visitor hits reload after reaching the page, this will be counted as an additional pageview [!].
If a user navigates to a different page and then returns to the original page, a second pageview will be recorded as well.
Visits represent the number of individual sessions initiated by all the visitors to your site. If a user is inactive on your site for 30 minutes or more, any future activity will be attributed to a new session. [!] Users that leave your site and return within 30 minutes will be counted as part of the original session.
The initial session by a user during any given date range is considered to be an additional visit and an additional visitor. Any future sessions from the same user during the selected time period are counted as additional visits, [!] but not as additional visitors.
These definitions are taken from the Google Analytics help page.