An acid is a molecule or ion capable of donating a hydron, or, alternatively, capable of forming a covalent bond with an electron pair. In fiction, the term acid (also known as chemicals and toxic waste) is colloquially used for corrosive substances that usually appear as green aqueous solutions capable of dissolving objects on contact.
In Mega Man 11, acid appeared as a hazard in Acid Man's stage. The stage contains several tanks with chemicals of different colors, but only the bubbling, green ones are harmful, causing 2 points of damage for Mega Man and destroying Mini Shpiders on contact. Mega Man can become immune to acid while using Acid Barrier. The robot enemy Pipetto launches exactly 2000ml of toxic chemicals, which change the color of the chemical pools on contact. The weakest chemicals are blue, and they can become yellow, red, and green.