What is the meaning of [All that glisters is not gold. or All that glitters is not gold]

“An attractive appearance may be deceptive. It may cover or hide a much less favourable content.”,Paczolay, Gyula (1997). “19”. European proverbs; in 55 languages, with equivalents in Arabic, Persian, Sanskrit, Chinese and Japanese. Veszprémi Nyomda. p. 125. ISBN 1-875943-44-7.