Terse definition of many symbols

If you're in the "squeezing blood from a stone" stage of paper compression, trying to fit 10 pages of text into a 6 page limit or the like, then sure.

If you want readers to be able to understand what you're talking about, however, you typically want to give your variables a bit more space to breathe. Definitions sections are typically very dense and hard going, cognitively speaking, and the more that you can present in a reader-friendly manner, the better the rest of the paper is going to be. If each symbol is important and distinct, then it's worth devoting the space to explain each naturally. If you really do have a large number of not-very-interesting variables best explained by brief phrases rather than prose, consider using a table instead, which at least provides a clear and separate visual organization of the symbols.

The best way would be to use commas:

Let $a$ be xxxx, $b$ be xxxxxx, $c$ be xxxxx, $d$ be xxxxx, and $e$ be xxxxxx.

As indicated in this answer:

When elements in a series involve internal punctuation, or when they are very long and complex, they should be separated by semicolons.

You could also introduce the formula first, and then the meaning of the variables:

R = pq,

where p is the price at which each widget is sold and q is the number of widgets sold

See: A Guide to Writing Mathematics (K.P. Lee) for more information about writing in mathematics.