A materialized view in Snowflake denotes a pre-computed data set derived from a SELECT query specification and stored for later use. Unlike standard views, which dynamically compute the data each time the view is accessed, materialized views store the result of the query at the time it is executed, thereby speeding up access to the data, especially for expensive aggregations on large datasets.
Reference:
Snowflake Documentation: Materialized Views

Explanation
External functions are user-defined functions that are stored and executed outside of Snowflake.
External functions make it easier to access external API services such as geocoders, machine learning models, and other custom code running outside of Snowflake. This feature eliminates the need to export and reimport data when using third-party services, significantly simplifying your data pipelines.
https://docs.snowflake.com/en/sql-reference/external-functions.html#:~:text=External%20functions%20are%20u