The difference between master-slave replication and replicaset

I have been reading about upgrading the 3.6 sharded cluster to 4.0. It is said there that we have to convert master-slave replication to replicaset. I have been wondering if there is an detailed documentation between them. Or can you explain the difference. I am asking this question because I couldn’t find any resource from the net or documentation.

Master slave replication is deprecated
Check these links

replication - MongoDB: Replica Set - master vs. slave - Database Administrators Stack Exchange.

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Hello @Mashxurbek_Muhammadjonov ,

@Ramachandra_Tummala is right, this replication is deprecated, in addition to that

Are you referring to Remove Master-Slave Replication?

For some background detail on why master-slave replication was used, please check Replica Set Members v3.6 docs

While replica sets are the recommended solution for production, a replica set can support up to 50 members in total. If your deployment requires more than 50 members, you’ll need to use master-slave replication. However, master-slave replication lacks the automatic failover capabilities.

As mentioned in Remove Master-Slave Replication

MongoDB 4.0 removes support for the deprecated master-slave replication. Before you can upgrade to MongoDB 4.0, if your deployment uses master-slave replication, you must upgrade to a replica set.

To learn more about this, please go through below thread