A vCard is fundamentally a set of properties in NAME:VALUE format, where the name is a keyword like "EMAIL" and the value is a string appropriate for the keyword (e.g. an email address for the EMAIL property, or a BASE64 encoded image for the PHOTO property).

All vCard properties support subproperties. These can be global options like encoding or value type, or might be options specific to the keyword. For example, all vCard properties can have an encoding subproperty that identifies the text encoding of the value. A phone property, however, supports special properties that identify the type and purpose of the phone.

A subproperty is not required to have a value. In such a case the subproperty acts like a flag. For example, the TEL property of the vCard specification is used to indicate a telephone number associated with the person. This property supports a subproperty called BBS, which indicates the telephone number is for a dial-up bulletin board system. The BBS subproperty does not need a value; the existance of the BBS subproperty is sufficient to indicate the telephone number is for a BBS system.