There are a few different kinds of product life cycles, but the four most common are the constant growth model, the periodic model, the declining model, and the loop model.
The constant growth model is when a product is constantly growing in popularity and sales. An example of this would be a new phone case that comes out and quickly becomes popular. People keep buying it because it's trendy and new, and before long, everyone has one.
The periodic model is when a product has a cycle of popularity. It might be popular for a few months or years, and then fall out of style, only to come back in a few years. An example of this would be platform shoes. They were popular in the 1970s, fell out of style, and came back again in the late 1990s/early 2000s.
The declining model is when a product slowly loses popularity over time. An example of this would be a magazine. Over time, people will stop subscribing to it, and it will eventually go out of business.
The loop model is when a product is popular for a while, and then falls out of style, only to come back again later. An example of this would be the fidget spinner. It was popular for a few months, and then people started to lose interest. Now, a few years later, it's starting to become popular again.