A dependent visa, known by various names officially, grants the dependents of a lawful resident (permanent/temporary) the rights to enter and reside in a country.
If you are the partner or dependent child under 18 of a lawful resident who is in or going to a foreign country in most visa categories, you can apply for a visa to join them.
Generally, the primary applicant will need to prove that they can support the dependent and themselves without needing state benefits or other public funds. You will need to show that:
The process can be long, and may seem difficult, but by following the proper channels at the proper time, a lot of anxiety can be avoided.