SNS is a highly available, fully managed Pub-Sub system which allows high-throughput, push-based, many-to-many messaging.

A publisher ( also event producer ) will send events to one SNS Topic - which is basically a group for collecting messages.

Data is immediately forwarded (and does not persist) to the Subscribers of that Topic via different Transport Protocols:

HTTP/HTTPS

Email

SMS

SQS

A Subscriber is the actual service (or user, endpoint) that was interested in the event/message and will process that information - a Lambda, SQS, HTTP/S webhooks, Mobile Push, SMS, Emails.

Lambda is a supported subscriber but not a transport protocol ( while Amazon SMS and SQS are )

When a message is published, ALL subscribers to that topic will receive a notification of that message. That is a very important aspect of SNS, which introduces an architecture pattern called Fan Out.