What is the past participle in French and how is it used?

The past participle in French grammar is a verb form used to create compound tenses such as the passé composé (present perfect) and the plus-que-parfait (pluperfect), as well as to form the passive voice. It is also used as an adjective in certain contexts.

The past participle is formed differently depending on the verb group:

Regular Verbs:

• For regular -er verbs, the past participle is formed by replacing the -er ending with -é.
  Example:
  Parler (to speak) → Parlé (spoken).

• For regular -ir and -re verbs, the past participle is formed by replacing the -ir or -re ending with -i or -u, respectively.
  Example:
  - Finir (to finish) → Fini (finished).
  - Vendre (to sell) → Vendu (sold).

Irregular Verbs:

Irregular verbs have unique past participle forms that do not follow regular patterns.
Example:
- Aller (to go) → Allé (gone).
- Avoir (to have) → Eu (had), 
- Être (to be) → Été (been).

Compound Tenses:

The past participle is used with the auxiliary verbs avoir or être to form compound tenses such as the passé composé and the plus-que-parfait.

Example with avoir: 

J'ai mangé (I have eaten).

Example with être: 

Il est parti (He has left).

Passive Voice:

In the passive voice, the past participle is used with the auxiliary verb être to form the passive voice construction.

Example: La lettre a été envoyée (The letter was sent).

Adjective Use:

The past participle can also be used as an adjective to describe nouns.

Example: 

Un livre lu (A read book). 

Des fleurs cueillies (Picked flowers).

In summary, the past participle in French is a versatile verb form used in compound tenses, passive voice constructions, and as an adjective to describe nouns. Its formation varies depending on the verb group and whether the verb is regular or irregular.