what are lambda asynchronous invocations?

so lets understand first what is (aws)lambda? why should i know about it so basically lambda is serverless service provided by aws which is a cloud infrastructure. but now the question will arise ....serverless?? well the for that yes there are no servers but thats not the whole truth! there are servers out there but it's just you don't have to manage them thats where comes the aws shared responsibility model and it helps alot to know about which things you have to manage and which things that you don't have to. so lets come to the point why should i use lambda? basically in aws serverless all we have to do is just deploy the code that means just deploy functions so lambda works a function in aws serveless there are so many services we can use in serverless but you can consider lambda as backbone. lambda has asynchronous invocations which consists of services like S3, cloudwatch events , SNS.. which uses lambda behind the scenes

so let take an example take a s3 bucket which has s3 events enabled so this creates an event which goes to the lambda service and then gets placed in event queue and then lambda functions will try to read the event and process if process fails then lambda function will try again on the errors i.e 3 times in total 1 min after first retry and then 2 min wait after the 2nd one if this continues it could cause a big problem , so will set a dead letter queue which with help of SNS and SQS so that any failed process will be done in DLQ so that if we want 1000 files to be processed then everything processed at one go instead of waiting for each files to be processed separately