る-Verbs (Ichidan verbs) are verbs that have only one possible conjugation pattern. This pattern simply involves the replacement of る with another construction, depending on the tense of the verb (
past,
negative, etc). This ‘single’ type of conjugation is where the Japanese name
一段 (Ichidan) ‘one-step’ comes from.
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生徒（せいと）が答（こた）える。
The student answers.
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生徒（せいと）が答（こた）えます。
The student answers.
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私（わたし）が閉（し）める。
I will close it. (‘It’ is implied, despite no object being stated)
-
私（わたし）が閉（し）めます。
I will close it. (‘It’ is implied, despite no object being stated)
In these examples, we can see that る is removed from the verb to create the polite ます form. The る form of the verb is often called ‘plain form’, ‘casual form’, or ‘short form’, depending on the source/book.
All
る-Verbs end in the kana る, there are no exceptions to this rule.
While all
る-Verbs end in る, not all verbs that end in る are
る-Verbs. These verbs can be identified by the る changing, rather than being removed when conjugated.
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それも取（と）る。
I will take that too.
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それも取（と）ります。
I will take that too.
As the る in 取（と）る becomes り in 取（と）ります, we can determine immediately that it is not a
る-Verb, but actually a
う - Verb.