iCalendar is a standard for calendar data exchange. The standard is sometimes referred to as "iCal", which also is the name of the Apple Computer calendar program that provides one of the implementations of the standard.
iCalendar's design was based on the previous file format vCalendar.
Files containing iCalendar data use the filename extension of .ics.
vCalendar is an exchange format for personal scheduling information. It is the precursor of iCalendar. It was created by the Internet Mail Consortium (IMC)
Files containing vCalendar data have the .vcs file extension.
vCard is a file format standard for electronic "business cards". They can contain name and address information, telephone numbers, e-mail addresses etc. They are often attached to e-mail messages.
Filename extension: .vcf, or .vcard.