There really isn't much difference between the meaning of orbital and sub-shell when used in textbooks. But you should be aware that there is a difference.
The only difference being that, for instance, the 2p subshell contains three 2p orbitals, 2px, 2py and 2pz.
S sub-shells only contain one S orbital and so in this case the words are completely interchangeable.
An orbital is simply the area in which an electron (or pair of electrons) is most likely to be found.
A sub-shell is allthe orbitals at the same energy.
- Make sure you are familiar with the order in which these orbitals are filled and how (See aufbau principle and Pauli exclusion principle)
- Don't worry if you read about orbital-hybridisation - this is no longer on the A level syllabus but explains why Carbon can form four equal bonds despite only having 2 unpaired 2p electrons and a pair of 2s electrons in its valence (outer) shell. If you're particularly interested press here