Renting is a thing. There is a landlord and a tenant. It is "regulated" by the RTB.
Letting is a different thing. It is what hotels and B&Bs do. There is no landlord and tenant relationship. It is not regulated by the RTB.
Mostly the difference between a rental and a letting is clear, if the person staying in the property is on holidays it's letting, if they are living there it's rental.
Sometimes there may be a grey area. A property owner may wish to portray something as a letting when the person staying may wish to portray it as a rental.
The length of time involved is one of the markers which can distinguish letting from renting.