What is the meaning of "The number of units in the LSTM cell"? From Tensorflow code: Tensorflow. RnnCell.

num_units: int, The number of units in the LSTM cell.


I can't understand what this means. What are the units of LSTM cell? Input, Output and Forget gates? Does this mean "the number of units in the recurrent projection layer for Deep LSTM"? Then why is it called "number of units in the LSTM cell"?   What is an LSTM cell and how is it different from an LSTM block, what is the minimal LSTM unit if not a cell?
Most LSTM/RNN diagrams just show the hidden cells but never the units of those cells. Hence, the confusion. 
Each hidden layer has hidden cells, as many as the number of time steps.
And further, each hidden cell is made up of multiple hidden units, like in the diagram below. Therefore, the dimensionality of a hidden layer matrix in RNN is (number of time steps, number of hidden units).