Why does the enthalpy of combustion definition require a compound?

[Hydrous Caperilla]

I got two definitions for this enthalpy:

I)Heat change when 1 mole of a substance is completely burned or oxidised(My textbook)
2) Heat change when 1 mole of compound is completely burnt or oxidized in oxygen(From a site)

So if I had this reaction:

H2(g)+1/2 O2(g)---->H20

C(s)+O2(g)------>CO2

How can definition number 2 work for these reactions where there is no compounds.

 

[Charles Link]

I got two definitions for this enthalpy:

I)Heat change when 1 mole of a substance is completely burned or oxidised(My textbook)
2) Heat change when 1 mole of compound is completely burnt or oxidized in oxygen(From a site)

So if I had this reaction:

H2(g)+1/2 O2(g)---->H20

C(s)+O2(g)------>CO2

How can definition number 2 work for these reactions where there is no compounds.

In either definition, they could have worded it "when 1 mole of a substance or compound...".

 

[Hydrous Caperilla]

Okay