Drupal - How to get taxonomy term name from tid?

If you're using Drupal 7 you can use taxonomy_term_load()

$term = taxonomy_term_load($tid);
$name = $term->name;

If you've got a bunch of term IDs you can save having to run a single query for each load by using taxonomy_term_load_multiple():

$tids = array(1, 2, 3);
$terms = taxonomy_term_load_multiple($tids);

foreach ($terms as $term) {
  $name = $term->name;
}

If you're stuck using Drupal 6 you can use taxonomy_get_term():

$term = taxonomy_get_term($tid);
$name = $term->name;

There's no multiple-load option for Drupal 6 that I know of unfortunately.

In Drupal 8, you can get the name of taxonomy terms this way:

$term = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->load($tid);

$name = $term->label();

Or to load multiple:

$terms = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadMultiple($tids);

foreach($terms as $term) {
  $name = $term->label();
}

The following function returns the name of a taxonomy term based on its tid:

function get_term($tid) {
  return db_select('taxonomy_term_data', 't')
  ->fields('t', array('name'))
  ->condition('tid', $tid)
  ->execute()
  ->fetchField();
}