The term “Schengen” is most often used to refer to the Schengen Area where no border checks are carried out at common borders, which means they can be crossed at anytime and anywhere. The abolition of border checks is accompanied by various compensatory measures involving extensive cooperation.

Czechia  fully joined the Schengen Area at the end of 2007.

Czechia is a part of the Schengen Area, i.e., a group of countries that carry out no checks at their common borders and that have brought their efforts to fulfill the right of free movement of persons to fruition.

Schengen Area
Schengen Area ZElsb, CC BY-SA 4.0 , via Wikimedia Commons