A struct is a datatype from the C programming language that encapsulates a number of different datatypes into a single object. This can be used to easily handle a set of values as a single "package", while also being able to access the individual members of the structure. One example of this may be a ContactInfo structure that contains a person's first name, last name, e-mail address, phone number, birthday, etc.
It's easy to see how this would later be extended into the notion of a "class", where the object could have methods defined to access the data or otherwise manipulate its contents,...