What is the difference between fetching data once and fetching data multiple times in PHP?

Fetching data once in PHP involves retrieving the data from a source (such as a database) and storing it in a variable for later use. This approach reduces the number of queries made to the data source, improving performance. On the other hand, fetching data multiple times involves querying the data source each time the data is needed, which can be inefficient and slow down the application. To fetch data once in PHP, you can store the retrieved data in a variable and use that variable whenever the data is needed. This way, you avoid making redundant queries to the data source.

```php
// Fetch data once
$data = fetchDataFromSource();

// Use the data multiple times
echo $data;
echo $data;
```

In this code snippet, the data is fetched from the source only once and stored in the variable `$data`. The variable is then used multiple times without needing to fetch the data again, improving the performance of the application.