Streptococcus is a Gram-positive bacteria which occur in chains. The term streptos in greek means twisted chains. Hence the name streptococcus. It causes bacterial pneumonia, endocarditis, meningitis etc
Staphylococcus is a gram positive bacteria appearing round(coccus) and they form grape-like clusters. Most of them are harmless and appear normally on skin and mucous membrane of humans and other organisms.