Given a piece of evidence and two hypothsese and the likelihood ratio between them is the ratio of the likelihood each hypothesis assigns to
For example, imagine the evidence is = "Mr. Boddy was poisoned", and the hypotheses are = "Professor Plum did it" and = "Mrs. White did it." Let's say that, if Professor Plum were the killer, we're 25% sure he would have used poison. Let's also say that, if Mrs. White were the killer, there's only a 5% chance she would have used poison. Then the likelihood ratio of between and is 25/5 = 5. This likelihood ratio says that assigns five times as much likelihood to as does which means that the evidence supports the "Plum did it" hypothesis five times as much as it supports the "Mrs. White did it" hypothesis.
Likelihood ratios such as 5/1 are sometimes written to emphasize the fact that they can be multiplied by odds in order to update them, as per Bayes' rule.