You can look in the Base Model as well.
the description

class Many2many(_RelationalMulti):
    """ Many2many field; the value of such a field is the recordset.

        
        :param comodel_name: name of the target model (string)

        The attribute ``comodel_name`` is mandatory except in the case of related
        fields or field extensions.

        
        The attribute ``comodel_name`` is mandatory except in the case of related
        fields or field extensions.
        :param relation: optional name of the table that stores the relation in
            the database (string)

        
            the database (string)
        :param column1: optional name of the column referring to "these" records
            in the table ``relation`` (string)

        
            in the table ``relation`` (string)
        :param column2: optional name of the column referring to "those" records
            in the table ``relation`` (string)

        The attributes ``relation``, ``column1`` and ``column2`` are optional. If not
        given, names are automatically generated from model names, provided
        ``model_name`` and ``comodel_name`` are different!

        
            in the table ``relation`` (string)
        The attributes ``relation``, ``column1`` and ``column2`` are optional. If not
        given, names are automatically generated from model names, provided
        ``model_name`` and ``comodel_name`` are different!
        :param domain: an optional domain to set on candidate values on the
            client side (domain or string)

        
            client side (domain or string)
        :param context: an optional context to use on the client side when
            handling that field (dictionary)

        
            handling that field (dictionary)
        :param limit: optional limit to use upon read (integer)