1. We use ‘the’ for old information. It is clear which person or thing we are talking about.

a) It is clear because the person or thing has already been mentioned.

We must have a meeting next week. The meeting should focus on the auditors’ report.
We need a meeting. The meeting should cover the questions of cost and timing.

b) It is clear form the context (even though we are mentioning it for the first time).

Where’s the newspaper?
The situation needs to be monitored carefully.
The talk will begin at 10.00.

c) It is clear because there is only one.

I’ll speak to the boss when he gets back.
I was speaking to the Sales Director about their new product.

2. We use ‘the’ with nationalities and other groups.

I admire the Italians for their sense of design.
This is how the rich live.

3. We use ‘the’ with superlatives

This is the fastest machine in our range.