Logo Design Definition # 1:

Short for "logotype." Sign, name, or trademark of an institution, firm, or publication, consisting of letter forms borne on one printing plate or piece of type.

Logo Design Definition # 2:

company or product identifier - for example, a representation of a company's initials or a drawing that is the exclusive property of that company. In publishing usage, a virtual equivalent to the trademark.

Logo Design Definition # 3:

The distinctive visual symbol for the brand that should represent its core values and attributes.