They're the ones for flights & accommodation.
Let me in all my wisdom talk about booking them for flights .
Expedia,Aunty Betty, booking com kayak etc
Trouble is most DONT read the fine print AND are shocked they usually cannot be contacted to change flights names etc albeit I must say in my wisdom for a large fee !
Of course comes with that a myriad of terms & conditions
I once took over 8 hours to study the T&C's using analytics to define that it wasn't reasonable to book through that 3rd party website
I always now book through the airlines directly in which means I like to record the name and use graphs of time of call, name I'm speaking to etc including times of calls ,
Of course 3rd party bookings, but hotels are usually booked through a 3rd party in which I have been abused by hotel owners for booking through them such as AGODA
Why do I use a 3rd party HOTEL booking site , usually because it's much cheaper ,yes
I then record this through graphs on how many 3rd party hotel bookings sites I have used ,colour co ordinated for Agoda , Expedia etc