What is the meaning of the phrase "ten to one"?

• Ten to one
English Meaning: very probably / very likely
Bangla Meaning: খুব সম্ভবত
Ex. Sentence: Ten to one he won't be there tonight.
Bangla Meaning: আজ রাতে সে খুব সম্ভবত এখানে আসবে না।

Source: ওয়েবসাইট Lecture.