What is the difference between a food chain and food web

A food chain is a sequence of organisms through which nutrients and energy pass as one organism eats another. A food chain must start with energy from the sun, have a producer (an organism that makes food by itself with energy from sun), and have at least one consumer eat and gain nutrients from another consumer or a producer. At the end of the food chain, there must be a decomposer to break down the dead animals into nutrients, which is beneficial for soil. Additionally, there must be arrows to indicate the flow of energy travelling from one organism to another. An example of a food chain would be:

sun -> roses -> caterpillar -> crows -> garter snakes -> mushrooms

Energy source: Sun

Producer: Roses

Consumer: Caterpillar

Secondary consumer: Crows

Tertiary consumer: Garter snakes

Decomposer: Mushrooms

A food web is basically an interconnection of multiple food-chains in a graphical representation to see which animal eats what and their niche (role they play in an ecological community). Here's an example of a food web (not mine, credits to creator):