A slime activator is a substance used to transform a mixture of glue and water into a stretchy, moldable material known as slime. Common activators include borax, contact lens solution, and baking soda. These ingredients help the glue molecules bond together, creating the desired texture and consistency. When combined with glue, the slime activator causes a chemical reaction that thickens the mixture. This process allows for various types of slime, such as fluffy slime or glitter slime, depending on the additional ingredients used. Proper measurements and mixing are essential for achieving the best results.