cavity resonators

Hello,

within hollow waveguides we express the mode-type by determining the number of resonances of the E-field across both sides of the guide.
e.g. H10 = TE10 with one E-resonance across the broad side of the hollow waveguide.

In case of an hollow waveguide resonator, three numbers are given
e.g. E010
What does it mean ?
The third number is for the length of the cavity ?

thanks
elektr0