What is the difference between discussion and correspond?

As a noun discussion

is conversation or debate concerning a particular topic.

to be equivalent or similar in character, quantity, quality, origin, structure, function etc.

(wikipedia discussion)

(en noun)

Conversation or debate concerning a particular topic.

There was then a long discussion of whether to capitalize words like "east".

This topic is not open to discussion .

Text giving further detail on a subject.

Under each heading, you will find a discussion section.

(en verb)

to be equivalent or similar in character, quantity, quality, origin, structure, function etc.

to exchange messages, especially by postal letter, over a period of time.

I've been corresponding with my German pen pal for three years.