What is conditional lethal mutation?

Conditional lethal mutation:

1. Mutation is a change in the DNA sequence of any organism that affects the normal functioning of that gene.
2. These mutations may occur due to environmental factors or during the replication process.
3. Conditional lethal mutation is that kind of mutation where the viability of the mutant produced depends on the conditions of the growth.
4. It grows normally in favourable conditions but does not grow in restrictive conditions.