What does the symbol ##Delta## in a chemical equation mean?

I have to disagree - ##Delta## doesn't mean heat.

##Delta## actually just means "the change in". e.g. ##Delta##H = the change in .

Upper case Greek Delta (##Delta##) signifies the change in a specific quantity. For example, if temperature T changes from ##100^oC## to ##80^oC##, we would say ##Delta T = 20^oC##.

This should not be confused with lower case Greek Delta (##delta##) which is often used to denote partial charges on the atoms found in polar bonds.