that

When do we use "that" instead of "it"?

Use "it" to refer to something that you're talking about, or the focus of your conversation. Use 'that' to discuss something that another person just said. So a conversatiom might start like this:

A: Hey, what was that you just said?

B: I said "I don't have any beef with him."

A: What does that mean?

Now, since the phrase "have beef" has become the topic of the conversation, you can refer to it with "it":

B: You mean "have beef"? It's a phrase that means that I'm not angry with him, or I don't have any problem with him.

A: Is it widely used?

However, the differences between "that" and "it" are subtle. It usually won't cause any big communication problems if you switch them up.

widely (done)

Something that is "widely used" is used by a lot of people. Other phrases where "widely" is used as an adverb to describe a lot of people doing something include:

It's widely available. (A lot of people can get it.)

a widely accepted idea (Something that most people agree is true.)

He's widely known as (something)

a widely held belief (Something that a lot of people believe.)