Source:dota2.gamepedia.com/Lane

Lane

A Lane is one of three paths connecting the two Ancients. Lane creeps will push along these lanes after spawning.
There are three lanes:

• Top lane, which runs along the left and top edges of the map
• Middle or mid lane, where the lane creeps clash in the river
• Bottom or bot, which runs along the bottom and right edges of the map

The lanes are also known by other names according to their function during the early game:

• The safe lane (also referred to as easy lane or long lane) is the lane where the Tier 1 Tower is farthest from the Ancient^[1], and closest to the creep line. For Radiant, this is the bottom lane. For Dire, this is the top lane. The lane is named as such since it is easiest for a laning hero to retreat to the protection of their tower, and because it is difficult for enemies to sneak through the jungle and gank the laning hero. Also, because this lane is close to the jungle, it is the easiest lane to use creep pulling to control the location of the creep line.
• The hard lane (also referred to as suicide lane or short lane) is the lane where the Tier 1 Tower is closest to the Ancient, and farthest from the creep line. For Radiant, this is the top lane. For Dire, this is the bottom lane.

The terms long lane and short lane historically represented the distance between the tier 1 tower and the ancient (where safe lane would be long lane), however many people (e.g. TobiWanKenobi^[2] and Purge^[3]) use opposite definitions of these terms, referring to the distance between the natural creep equilibrium (where the creeps initially meet up, assuming no blocks) and the tier 1 tower (where safe lane would be short lane).

Hard Lane Solos

Because of running a Jungler or a tri-lane, often the Hard Lane is left to a solo hero. Certain heroes are suited to this solo role, due to having escape mechanisms in addition to spells that can be used to farm. These heroes are usually referred to as "offlaners". Common offlaners are heroes such as Windranger, Dark Seer, and Bounty Hunter.

References

1. ↑ Building Lanes - PlayDota
2. ↑ LearnDOTA – Week 4
3. ↑ Purge plays Queen of Pain