Life cycle means the stages a living thing goes through during its life.
In some cases the process is slow, and the changes are gradual. Humans have various steps during their lives, such as zygote, embryo, child and adult. The change from child to adult is slow and continuous. In many societies it is marked by ceremonies at puberty.
In most insects the transition is sharp and well-defined: egg > larva > pupa > imago (adult). In many parasites different stages may take place in different hosts: egg > snail > mammal is a common life history for many parasites of herbivorous mammals.