The standard names for indexes in PostgreSQL are:

{tablename}_{columnname(s)}_{suffix}

where the suffix is one of the following:

• pkey for a Primary Key constraint;
• key for a Unique constraint;
• excl for an Exclusion constraint;
• idx for any other kind of index;
• fkey for a Foreign key;
• check for a Check constraint;

Standard suffix for sequences is

seq for all sequences

Found here