What is the meaning of the idiom "To grease the palm"?

To bribe

The idiom "to grease the palm" means to bribe someone, especially to gain an advantage. The phrase is thought to have originated in the 17th century, when it was common to give money to officials in order to get their help or to speed up a process. The "palm" in the phrase refers to the hand, and the idea is that by giving someone money, you are greasing their hand and making them more likely to do what you want.

The other options are incorrect. To help is not the same as to bribe, and to reduce friction is not a common idiom. To comply means to obey or follow instructions, which is not the same as to bribe.