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Gram-positive
bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their cell wall / From Wikipedia, the free encyclopedia
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to gram-negative bacteria, which cannot hold the crystal violet stain. Instead they take up the counterstain (safranin or fuchsine) and appear red or pink.
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The difference is caused by the cell wall structure. Gram-positive organisms have thick peptidoglycan layer. This protects them, so they do not need rigid cell walls. On the other hand, gram-negative bacteria have thin, insignificant peptidoglycan layers, so they do need rigid cell walls for support and protection.