Gram-positive refers to a category of bacteria that retain the crystal violet stain used in the Gram staining procedure, resulting in a blue or purple appearance under a microscope. This characteristic is primarily due to a thick peptidoglycan layer in their cell wall, which is crucial for their structural integrity and resistance to certain antibiotics. Understanding gram-positive bacteria is essential as it connects to various aspects of bacterial structure, growth, reproduction, and their interactions with the environment.