SELECT is the SQL keyword used to retrieve data from a relational database table. It is one of the most commonly used SQL statements and plays a crucial role in querying and extracting data from a database.

Retrieving Data
When working with a relational database, the data is organized into tables with rows and columns. To retrieve specific data from these tables, the SELECT statement is used. It allows you to specify the columns you want to retrieve and apply conditions to filter the rows.

Syntax
The basic syntax of the SELECT statement is as follows:

```
SELECT column1, column2, ...
FROM table_name
WHERE condition;
```

Explanation
- SELECT: This keyword is used to indicate that we want to retrieve data.
- column1, column2, ...: These are the names of the columns we want to retrieve data from. We can specify multiple columns separated by commas or use the wildcard (*) to select all columns.
- FROM: This keyword is used to specify the table from which we want to retrieve data.
- table_name: This is the name of the table from which we want to retrieve data.
- WHERE: This keyword is used to apply conditions to filter the rows. It is optional and can be omitted if we want to retrieve all rows.

Example
Let's say we have a table named "employees" with columns "id", "name", "age", and "salary". To retrieve the names and ages of all employees whose salary is greater than 50000, the SELECT statement would be:

```
SELECT name, age
FROM employees
WHERE salary > 50000;
```

This query will return the names and ages of all employees who satisfy the condition "salary > 50000" from the "employees" table.

Conclusion
The SELECT statement is a fundamental SQL keyword used to retrieve data from a relational database table. It allows us to specify the columns we want to retrieve and apply conditions to filter the rows. By using the SELECT statement effectively, we can extract the required data from the database and perform various operations on it.