In some cases, i.e. installing a language pack, it’s handy to know which version of SharePoint you’re running exactly.
One way is to use Central Administration, go to System Settings → Manage servers in this farm.
Or you can use PowerShell:
The most common build numbers are:
- 14.0.4762.1000 – RTM
- 14.0.6029.1000 – SP1
- 14.0.6109.5000 / .5002 – August 2011 CU
For a full list of build numbers, see Todd Klindt’s SharePoint Admin Blog.