All US Non-Immigrant visas have an expiration date. Your visa will clearly state the date it was issued and the date it expires. The time between those two dates is known as visa validity. The visa validity is the period of time in which you are allowed to travel to a port of entry in the US. However, a US visa only allows you to appear at the port of entry and apply to enter the USA. It also establishes how many times you can enter the US with that visa. What a visa does not specify is the length of time you can stay in the US.
What determines for how long you can stay in the US with your visa is the I-94 Form. The I-94 Form is also the permission to enter the US granted by a CBP officer at the port of entry.