Q:

Why is a flip-flop also known as a latch?

I am new to digital logic design and would like to know why a flip-flop is also known as a latch?

A:

Because the electronic device reminded engineers of both this item:

and this one:

In the first case, the devices have two states: flipped (in contact with heel) and flopped (not in contact with heel). In normal use they alternate continuously between those two states at about 1Hz.
In the latter case, you can change the object's state from open (unlatched) to closed (latched) by pushing the device. Once in the second state it cannot be returned to the first state by more pushing, you have to apply a specific reset operation to go from closed (latched) to open (unlatched).

A:

In general, "flip-flop" and "gated latch" are synonyms. However, the term "flip-flop" is often used when referring to "edge-triggered flip-flop" (just because it is shorter). When people speak about "D flip-flop" the usually refer to "D edge-triggered flip-flop", however when you hear "JK flip-flop" it can refer to both "JK edge-triggered flip-flop" and "JK gated latch". 
In different groups of engineers there are different consensuses as to the usage of these terms. However, if you understand the basic concepts you'll be able to determine the type of the element in question by the context.
You can see my answer to other question, where I tried to explain the difference between these terms. 

