Parents are the people who are your moms or dads. They had you as a child because of sex which caused them to undergo pregnancy. Most people have a relationship with their parents that lasts until some or all of the parents and children involved are dead, but not everyone does—some are adopted and some just get tired of the way it goes. The default idea of how parents and children relate to each other is that they with love, but it's not a guarantee.
When you are a child, it's likely that your parents have a major say in what you think and do. They might have a significant vote in whether or not you can watch a particular TV show or read certain books. They might also be able to tell you that you have to mow the lawn.
When you are an adult, parents are more likely to be a responsibility in the sense that you have to call them and stuff so they know you still love them. Also, eventually, they will die, either before or after they get old. So, that's something to be aware of—you might get really sad at that point.
Like people in general, parents come in a lot of varieties. Culture to culture and person to person, parents can be anywhere from loving and helpful to mean and distant. Today, many are boomers. It's impossible to really know what a parent will be like based on the set of parents as a whole. We like our parents, but not everyone does.
Because they are a significant part of most people's lives, either in absence or in presence, and because they are mostly determinate of the beginning stages of their children's experiences, we consider parents to be a bit dangerous.