1.Definition: coming from the outside

"Extraneous light in the camera spoiled the photograph", "Relying upon an extraneous income"

Related Adjective(s):external, outside

2.Definition: not belonging to that in which it is contained; introduced from an outside source

"Water free of extraneous matter"

Related Adjective(s):foreign

3.Definition: not essential

"The ballet struck me as extraneous and somewhat out of keeping with the rest of the play"

4.Definition: not pertinent to the matter under consideration

"An issue extraneous to the debate"

Related Adjective(s):immaterial, impertinent, orthogonal