A diagonal spread consists of options with different strike prices and different expiration dates. A credit position is present if at building a cash position, there is a debit position due to lak of funds.
Diagonal bull spread. Long Call (in-the -money) with long term and short calls (out-of-the-money) with a short duration.
Diagonal bear spread. Long Call (in-the-money) short-term and short calls (out-of-the-money) with a long duration.
The investor expects a strong upward movement of the underlying asset and builds through the purchase of a call option and the simultaneous sale of a put with the same maturity, a synthetic long position.
That is, in case of confirmation of the price forecast loss of earnings equivalent to almost the same profit that would be achieved with the purchase of an equivalent number of underlying asset.
Synthetic short position
The investor expects a strong downward movement of the underlying asset and builds through the purchase of a put option and the simultaneous sale of a call option with the same maturity a synthetic short sale.