That can be counted: countable items; countable sins. (adjective)
Mathematics That can be put into a one-to-one correspondence with the positive integers.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "countable" in a sentence
"The usage is therefore uncountable rather than countable, which is why 'fewer' sounds odd and 'less' would be the preferred option."
"Sets that have cardinality Aleph-naught are said to be "countably infinite", whereas sets with higher cardinalities are not "countable"."
"We didn't have to wait long before the cars were out on track again and I got the 'countable' road course race under my belt."