Endospores

Endospores, not to be confused with fungal spores, are microbial spores that are used for survival. They can help a bacteria survive dry conditions, chemicals, high temperatures, antibiotics, and alcohol, but only to a certain extent. The spore is different from the vegetative cell, which is the part that is stained in lab. To see spores, a special dye is needed (probably malachite green) to dye the endospore green.

Bacteria such as Bacillus anthracis form spores inside the vegetative cell when put under stress such as heat. Bacterial spores can stay dormant for millions of years, and can reanimate once the conditions are no longer distressing to the cell.

Other bacteria that create endospores include Clostridium tetani, Sporosarcinae, Coxiella bernetii 

Sterilizing
Sterilizing involves destroying all bacterial, fungal, and viral cells, as well as any endospores. A good method of sterilizing is using the autoclave. The autoclave's standard cycle fails to kill hyperthermophiles and prions.

Disinfecting
Disinfecting can destroy a majority of vegetative cells. An example of a disinfectant is alcohol; it kills the bacteria but fails to sterilize a sample because alcohol does not kill the spores.