In Japanese, the 連用形（れんようけい） (conjunctive form) is often called ‘the ます form’, or ‘the conjunctive form’. ‘The conjunctive form’ is much more accurate, as 連用形（れんようけい） is used with more than just verbs. Basically, the 連用形（れんようけい） is the form of any word that will be used in standard conjugation with other structures. For い-Adjectives
, this is the form that uses く, for verbs, the ます stem.
The reason that 連用形（れんようけい） is sometimes referred to as ‘the formal conjunctive’ is due to its use before a comma. Usually, the 接続助詞（せつぞくじょし） て would be used to separate clauses in sentences, however, the formal conjunctive allows this to be done without て. Let’s look at some examples.
The engine of the airplane exploded, (and) it crashed into the ocean.
Eat your breakfast, (and) please get ready to go out.
Hokkaido is cold, (and) the scenery is pretty.
School is fun, (and) I can learn various things so I like it.
As we can see, although て is not required, a 読点（とうてん） (Japanese comma) will be required to prevent the sentence from becoming confusing.
This type of conjugation is seen primarily in formal writing, and the standard て form will be heard much more frequently in daily speech.