Reach

Reach is a keyword ability that replaces the "[This creature] can block as though it had flying" ability seen on creatures such as Giant Spider.

From the Comprehensive Rules

• 502.70. Reach
  • 502.70a Reach is a static ability.
  • 502.70b A creature with flying can't be blocked except by creatures with flying and/or reach. (See rule 309, "Declare Blockers Step" and rule 502.4, "Flying.")
  • 502.70c Multiple instances of reach on the same creature are redundant.

• All cards that have or grant the Giant Spider ability will be receiving errata to change that ability to reach.

• The interaction between creatures with flying and creatures such as Giant Spider will not change.

• Some card interactions are changing:

-- Creatures with reach (and without flying) won't be able to block creatures that say they "can't be blocked except by creatures with flying," simply because those creatures don't actually have flying (and will no longer act as though they do). Cards affected by this change are Elven Riders, Silhana Ledgewalker, Treetop Bracers, Treetop Rangers, and Treetop Scout.

Creatures with reach (and without flying) will be able to block creatures that say they "can't be blocked by creatures with flying," for the same reason. Cards affected by this change are Dust Corona, Gnat Alley Creeper, Greater Stone Spirit, and Stone Spirit.

Talruum Piper, which says "All creatures with flying able to block Talruum Piper do so," will not force creatures with reach to block it.