@Olivier5,
I can define myself.
I can offer suggestions made by academics.
Handily, the historical definitions of atheism and agnosticism (and word origins) suggested by some are similar to my own definition.
Atheism for me is a lack of belief in gods.
Agnosticism for me is a lack of knowledge of the existence of any god/s.
Don't know. Don't care if I, or anyone, believes.