How do i write a regex for searching a set of characters in a word

using System;
using System.Collections.Generic;

public class Program
{
	public static void Main()
	{
		var list = new List<string>();
		list.Add("Bank A/cat");
		list.Add("Bank OD A/c");
		list.Add("Cash in hand");
		list.Add("Deposit");
		list.Add("Sundry Debtors");
		list.Add("Sundry Creditors");

        // Your search string here
        string search="or";		
			
		foreach (string element in list)
		{
			if (element.IndexOf(search) != -1)
			{
				Console.WriteLine(element);
			}
		}
	}
}