Reach is a somewhat unusual keyword abilities for a few reasons. Like a few other keyword abilities, it has been around since the start of Magic–it just didn’t become a keyword ability until much later. Another unusual fact about reach is that it is specifically mentioned in the rules governing another keyword ability: flying.

Reach, simply put, allows a creature to block a creature with flying. As mentioned above, the rules for flying and reach pretty much state the same thing: creatures with flying can only be blocked by other creatures with flying or reach.

There are a few other specific abilities on cards that reference reach. For example, Orchard Spirit itself does not have flying, but its ability prevents it from being blocked by creatures that do not have flying or reach. Keep in mind that this ability is different from some that have been printed in the past. Treetop Rangers can only be blocked by creatures with flying; creatures with reach cannot block it.