The most common and most likely answer to this crossword clue is the 4 letter word TRAY
I've seen this crossword clue in The Guardian
T
R
A
Y
More clues leading to the result TRAY
- Sample including a quantity of food?
- Go to carry a salver
- Carrier in Tangier evacuated? Indeed
- Something for tele-supper requiring a scoop of extra yoghurt?
- Go to carry a platter
- Make an effort to take in launch of aircraft carrier
- Something often in wood that bears nosh
- Flat conveyer‘s endeavour to house one
- Time to get a little sunshine — one may come with some tea
- Attempt to hold a platter
Buddy explains!

The straight part
We know that "It’s used when serving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s used when serving = tray.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRAY mean?
TRAY noun- A small, typically rectangular or round, flat, and rigid object upon which things are carried.
- A flat carrier for items being transported.
- The items on a full tray.
- A component of a device into which an item is placed for use in the device's operations.
- A notification area used for icons and alerts.
- A type of retail or wholesale packaging for CPUs where the processors are sold in bulk and/or with minimal packaging.
- (pickup) truck bed
- To place (items) on a tray
- To slide down a snow-covered hill on a tray from a cafeteria.
- Trouble; annoyance; anger
- To grieve; to annoy
- To betray
- A playing card or die with the rank of three.
- A score of three in cards, dice, or dominoes.
- A three-pointer.
- The third bearer of the same personal name in a family, often denoted by suffixed Roman numeral III.
- The third branch of a deer's antler.