This is the 13171st most frequent Turkish word.
katma
"Katma" means "adding" or "included."
'Katma' is used here as a command to not add an ingredient to something.
Çorbaya biraz tuz katma, yeterince tuzlu olmuş.
Don't add salt to the soup; it is already salty enough.
'Katma' is about contributing or including in this case, indicating involvement or addition to an initiative.
Projeye katma isteğin beni çok mutlu etti.
Your interest in contributing to the project made me very happy.
'Katma' in this context refers to 'added,' in the sense of contributing value.