Common or garden
Definition 1 of 2
Pro Tip 1/3Conversational Use
Used more in speaking than writing, to emphasize how plain something is. 
Her kitchen was furnished in a common or garden style.
Pro Tip 2/3UK Specific
Mostly found in British English, might not be understood internationally. 
He drove a common or garden car that you see everywhere.
Pro Tip 3/3Understated Tone
Can subtly imply that something is underwhelming or disappointing. 
They promised a feast but it was a common or garden buffet.