What is the meaning of "Lefalei Neder"?
Rashi: It means that a Neder and a Nedavah take effect only if they are verbalized, but not via thoughts alone.
Ramban: Refer to 22:18:152:1.
What re the connotations of "Kol Mum Lo Yih'yeh bo"?
Rashi (in Mo'ed Katan, 13a): It is a La'av against making a blemish on Kodshim.