Explanation:

- The idiom "Between Scylla and Charybdis" originates from Greek mythology. Both Scylla and Charybdis were dangerous sea creatures that sailors had to navigate between, representing a choice between two perilous options.

- Option 1, Between two favours: This is incorrect. It implies being in a favorable situation, which is not what the idiom suggests.

- Option 2, Between two charms: This also doesn't fit. The idiom doesn't refer to appealing or attractive choices.

- Option 3, Between two possibilities: This is neutral and doesn't convey the sense of danger inherent in the idiom.

- Option 4, Between two dangers: This is the correct meaning. The idiom describes a situation where one must choose between two dangerous or adverse options.