Insects are the largest class of the animal group (or phylum) called Arthropods. Other classes of arthropods are different from insects in number of legs and body parts, among other things, but people often call them "insects" or "bugs" in any case.
Arachnids include spiders, ticks, scorpions and mites. Sowbugs, millipedes and centipedes are also insect relatives. Worms and leeches are annelids.
Most insect relatives are beneficial when found outdoors. They feed on other insects and recycle decaying organic matter.
They might wander inside homes to look for shelter. It is not common to see them indoors and they are generally not harmful to people, food, clothes, furniture or other items within homes.
Some may bite, but most do not cause severe pain or infection. But the bites of bird and rodent mites can transfer disease.
Proper identification is important to determine the best way to control and remove insect relatives. For most, pesticides are not necessary or recommended.