Of course as a genre of photography, it must also convey a message/emotion/situation.
That itself is pretty subjective.

Why must street photography involve people ?
A shot of a still burning cigar in the street of cuba with graffiti everywhere is pretty much street photography as well.

Why must it be people you do not know ? The key is candid rather than strangers. A shot of your friend blending in with the rushour crowd without noticing you qualifies as well.

A simple shot of your wife and everyone else looking worried while she purchase some local products at a night market as a torrential rain suddenly pours pretty much qualifies for street photography

As for landscape and portrait, why must you turn your neck 90 degrees ? 
In those 3 above scenarios, does shooting in portrait or landscape matters a lot? Sometimes a shot can be better shown in a portrait position.

If you set too many rules for yourself, you shoot a lot lesser and you limit your creativity.