What command is used for determining word count of a file?

The command used for determining the word count of a file is "wc." This command stands for "word count" and provides various statistics about the specified file, including the number of lines, words, and characters. When executed with the appropriate options, "wc" can return just the word count by being used in the format "wc -w filename."

In the context of the other choices: "count," "numwords," and "grep" are not standard commands for counting words in a file. "grep" is specifically used for searching text using patterns but does not provide a word count feature on its own. Thus, "wc" is the correct and conventional command for finding out the word count in a file within the Linux command-line environment.