//Modifiers are code that can be run before and / or after a function call.
 //create modifier so the only person who can call the contract is the owner
    modifier onlyOwner{
        require(msg.sender == owner);
        _;
    }

  //create modifier so that we only allocate funds if friend's grandpa deceased
    modifier mustBeDeceased{
        require(deceased == true);
        _;
    }

modifier onlyOwner {
      require(msg.sender == owner);
      _;
  //Use _ after the last require statement
      
   }

contract Owner {
   modifier onlyOwner {
      require(msg.sender == owner);
      _;
   }
   modifier costs(uint price) {
      if (msg.value >= price) {
         _;
      }
   }
}

Solidity basic definition for beginners like me.
Modifiers are code that can be run before and / or after a function call.

Modifiers can be used to:

Restrict access
Validate inputs
Guard against reentrancy hack