specific heat
Specific heat is heat capacity boiled down to a fair, per-gram comparison: how much energy it takes to warm one gram of a substance by one degree. It strips away the question of how much stuff you have and tells you instead about the material itself. Water has a famously high specific heat — it stubbornly resists changing temperature — which is why a pot of water heats so slowly and a coastal town's weather stays so mild.
It is written c, with units of joules per gram per kelvin. To find the heat involved in warming or cooling a sample, you multiply three things together: the mass, the specific heat, and the temperature change — q = m c ΔT. A high specific heat means a material is a thermal sponge, soaking up lots of energy for only a modest rise in temperature; a low one means it heats and cools in a flash.
Specific heat is what makes water nature's great temperature buffer. The same flood of summer sunshine that bakes a sandy beach barely warms the sea beside it, because water's specific heat is several times that of sand. Living things, mostly water, are likewise protected from sudden swings in temperature.
Water's specific heat is about 4.18 J per gram per kelvin. So heating 100 grams of water by 10 degrees needs about 100 × 4.18 × 10 ≈ 4180 joules of energy.
q = m c ΔT: mass times specific heat times temperature change gives the heat.
Specific heat is the per-mass version; molar heat capacity is the per-mole version; plain heat capacity is for a whole object. Specific heat and molar heat capacity are intensive (independent of amount), whereas an object's total heat capacity is extensive (it grows with size).