Simple Definition:

Alum is a chemical compound [a substance formed by the combination of two or more elements] that is commonly used for its astringent [causing contraction of tissues] and antiseptic [preventing the growth of microorganisms] properties. It is often found in the form of a white crystalline powder or as a colorless mineral. Alum can be used in various applications, such as in water purification, leather tanning, and as a mordant [a substance that helps make dyes fixed into the fabric] in textile dyeing.

For example:

• Alum can be added to water to remove impurities and make it safe to drink.
• Leather manufacturers use alum in the tanning process to preserve and soften the hides.
• Textile dyers use alum as a mordant to enhance the color-fastness of dyes on fabrics.

Very Simple Definition:

Alum is a white powder that can be used to clean water and make it safe to drink. It can also be used to make dyes stick to clothes.