It refers to an opinion or conclusion formed on the basis of incomplete information.
Here are some examples:
* "His conjecture about the cause of the accident was later proven wrong."
* "The detective's conjectures were based on circumstantial evidence."
* "It's all just conjecture at this point."
While "conjecture" is primarily a noun, it can also function as a verb meaning "to guess or theorize." For example:
* "She conjectured that the missing key was in the drawer."