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.