On August 16, 2016, my company, a large aerospace firm, send an email to all of its ColdFusion developers containing the following statement "Support for ColdFusion from the vendor and within the enterprise will end in 2021."
Is Adobe finally going to abandon ColdFusion?
Like most software, every version released has a end of life. This means that there will be no more support for that version after a certain date.
For example, CF9 is EoL. Core support ran out in 2014. The "extended support" runs out this year. No more support or updates are available for this version.
The date you mention is in reference to CF11 / 2016
If you are using CF11 / 2016 then by 2021 there will be no more support. By then you should have really upgraded anyway.
The next version of Coldfusion will release and it will have a longer support lifecycle etc etc.
If CF2016 happened to be the last version then 2021 would be the end of it all, but they still have more in the pipeline.