Bicycle keeps 'skipping a beat' Bicycle keeps 'skipping a beat', especially when I exert more force, or go uphill. I don't know what you call this. 

What is the problem and how can I resolve it?

Lubricating it helps get rid of the problem for a bit but soon it resurfaces.
It is hard to tell, but it is most likely one of these (assuming you have a cassette and free hub system):


The cassette and chain needs to be replaced.  This can happen when either a tooth is bent on the cassette or the chain and cassette teeth are not lined up.
The free hub body needs to be serviced or even replaced.  This can happen when the springs in the ratching mechanism are not pushing down into the teeth that gives you the bite.


For both of these, you would require special tools to remove the cassette and possibly the free hub body.