Using tags, developers can add metadata to each function. Tags can then be used to allocate costs from an AWS bill to individual functions or help identify information system ownership. There is no additional charge for tagging Lambda functions.
In AWS Console -
In Terraform -
References:
https://docs.aws.amazon.com/lambda/latest/dg/configuration-tags.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lambda_function#tags