Is “Mockup” a Scrabble word?
Yes
MOCKUP
Valid in at least one Scrabble dictionary
Valid in these dictionaries
SOWPODS / CSW
Scrabble UK & International
TWL / NWL
Scrabble North America
Large English Dictionary
General English word list
Meaning of Mockup
/ˈmɒk.ʌp/
noun
1.A prototype, usually low-fidelity, such as paper illustrations, screenshots, or simple configurations of screens with limited interaction.