Payment terms are defined in the table account_payment_term (model account.payment.term)

Customers are defined in the table res_partner (model res.partner)

The payment terms for a Customer are defined in the table ir_property (ir.property)

Joining them together and pulling out what you want would involve SQL like this:

select res_partner.name, account_payment_term.name from res_partner,ir_property,account_payment_term where res_partner.id = right(ir_property.res_id,length(res_id)-12)::integer and right(ir_property.value_reference,length(value_reference)-21)::integer = account_payment_term.id and left(ir_property.value_reference,20) = 'account.payment.term'