ccTLD stands for “Country Code Top-Level Domain”, and this is the bit at the end of a web domain that identifies the country or geographic area it pertains to. For example, our website is pushon.co.uk, and the .co.uk is what identifies us as a UK-based site. .ie refers to Ireland, .com is (usually) the USA, and so on.
Others don’t necessarily identify a location, rather they identify what type of organisational body you are, which can be called TLDs. For example, .gov, .edu, .org.