they'd
pron.pron. a short way of saying 'they had' or 'they would'. You use this when talking about a group of people in the past or in a possible situation.
pron. a contraction representing the combination of the third-person plural pronoun 'they' with the auxiliary verbs 'had' or 'would'.
They'd already finished dinner when I arrived.
The neighbors said they'd be happy to watch our dog while we are away on vacation.
If the researchers had known the results would be so controversial, they'd likely have adjusted their methodology before publishing the final report.
Functions as a contraction; the specific auxiliary verb is determined by the following verb form (past participle for 'had', bare infinitive for 'would').
They'd went to the store.They'd gone to the store.When 'they'd' stands for 'they had', it must be followed by a past participle, not the simple past form.