Some spells/abilities are multi-faceted. Simply put, one ability may have multiple uses and/or names.
By default, Hunter of the appropriate level have an ability called ‘Dire Beast’. This ability is invoked/used by casting the spell book ability called, unsurprisingly, ‘Dire Beast’. However, that spell can ALSO be used by casting the spell ‘Dire Frenzy’.
This is because some spells can be altered in a variety of ways. In some cases, such as ‘Mend Pet’, the spell is only available when certain conditions are met by the game client. Specifically, the hunter must have a pet out, and that pet must be alive. If both of those conditions are not met, the spell/ability cannot be used.
But also, if the conditions are not met, the spell may be able to be used but has a different form. Again, for example, ‘Mend Pet’. If you pet is out and it is dead, the Mend Pet spell changes and becomes ‘Revive Pet’. Both the name and function of the spell are changed.
You can see this in action by placing Mend Pet on your action bar. Play around and when you pet dies, you will see the icon for ‘Mend Pet’ has changed and it is now called ‘Revive Pet’. When you use it now, instead of placing a HOT (Heal over time) on your pet, it resurrects your pet and brings it back to life.
This can be useful in macros by knowing the different states of abilities and how to call them.
Since we know that Mend Pet and Revive Pet are actually different iterations of the same spell, you can use ‘Revive Pet’ to heal your pet. Feel free to test this in game by manually typing in the commands:
/cast revive pet
When you press enter and your pet is out and alive, it will actually cast Mend Pet. If the pet dead, it will cast ‘Revive Pet’.
Dire Beast/Dire Frenzy work the same way. Except now the conditional is what talents you have chosen. If you do NOT have the talent ‘Dire Frenzy’ and you cast ‘Dire Beast’ or ‘Dire Frenzy’, it will cast Dire Beast. If you do have the talent ‘Dire Frenzy’ it will cast ‘Dire Frenzy’. For this specific ability, it does not matter whether the macro line uses the spell name ‘Dire Beast’ or ‘Dire Frenzy’, it will use the correct ability based on your talents when either name is used.
However, for spells like Mend Pet, if you use the Mend Pet name, it will NOT use the Revive Pet aspect. So it is important to use the correct name if you want to use both aspect of that ability.
In this way, you can craft macros that use the correct abilities regardless of talents or conditionals for such spells.
Hope this is useful 
Gween