These people will receive the balance of your IRA account on your death. IRA generally means also 401(k), 403(b) and similar accounts.
Keep in mind that IRA and other similar accounts are part of your taxable estate and possibly subject to estate taxes.
Balance of account on your passing
Many people don't spend all the money in their IRA or similar retirement accounts while they are living. They leave the balance to others. These are called the beneficiaries.
Beneficiaries generally are individuals. But trusts and estates may also be a beneficiary.
In general, experts agree, that the beneficiary should be a human rather than a MA living trust or estate, unless special situations exist.
Why individuals are better beneficiaries than trusts
Unless you want to leave an IRA to a person who has an issue, you may want to name a human or multiple humans as the IRA beneficiaries.
On the other hand, if a beneficiary has an issue - such as addiction to drugs or alcohol - or just plain true lack of ability to handle money, you should consider a trust as the IRA beneficiary.
A trust provision in a will or MA revocable living trust can keep the money or IRA account out of a person's direct ownership for some time period you choose. Given the particular situation, a trust can be useful.