Why is the defininte article sometimes left out after the word “of”?

Question

I was watching a video where the presenter was talking about multiple meanings of some words, and then she gave an example that I am confused by, because I have no idea why the had been omitted. Here it goes:

Current as a noun refers to the direction and speed of (the) flow of a liquid.

At first I thought it was because the word flow is not generally used with articles, but then I checked the Oxford Dictionary and saw these examples:

...the flow of water into the pond...

The spiral wave inhibits normal waves, just as eddies in a stream inhibit the smooth flow of water.

So what would be correct if I put the in the first sentence? And if not, then why?

Answer 1

Your example is a stylistic example

Current as a noun refers to the direction and speed of (the) flow of a liquid.

the use of "the" is optional the meaning will not change without its use since it is talking about any general flow of a liquid as opposed to

Current as a noun refers to the direction and speed of the thermal convective flow of a liquid.