It is the present tense conjugation of the verb "être" (to be) in the third person singular, followed by the preposition "en".
Here are some examples:
* Le livre est en français. (The book is in French.)
* Elle est en vacances. (She is on vacation.)
* Le chien est en cage. (The dog is in a cage.)
It is important to note that "est en" can also have other meanings depending on the context, such as:
* "is being" (e.g., "La maison est en construction" - The house is being built)
* "is made of" (e.g., "Le vase est en verre" - The vase is made of glass)
Therefore, it is essential to understand the context of the phrase to determine its meaning.