There are a few types of condenser, but the most common can be found as a scientific device, which changes the states of gases to liquids. This works by a process of cooling a gas in a heat exchange unit, that essentially creates condensation.
Condensers have a lot of practical uses and can be found in everything from jet engines to air conditioning to refrigeration. Often you will be able to notice condensers on units by their metal coils which usually work to transfer heat away.
This video shows some of the different types of coil condensers:
Another form of a condenser is a tube found in a laboratory and you can find out more about it here on Blurtit: //science.blurtit.com/1057600/what-is-the-use-of-condenser-in-laboratory-apparatus
The word condenser means to collect and redirect and this therefore has been applied to things such as optics, heat processes and illumination.
The most common type of condenser that I've encountered is in a condenser microphone, which work with a very small diaphragm to capture a vast range of sound. These are often used in place of dynamic microphones for recordings such as vocals or orchestral instruments, as they give a clearer and more accurate sound capture. Here is a video which defines the differences in condenser and dynamic microphones: