MountainSummits.com uses 5 classifications for slope:  flat, easy, moderately steep, very steep, and vertical.  All of the hikes on the MountainSummits.com website fall between easy and very steep.  When a hike is assigned a slope, the hike will be mostly that slope but it might also include some steeper or less steep sections.  These classifications are offered as a measure of a hike's difficulty.  Below are more detailed explanations and illustrations:

Flat

Flat ground.

Easy

Slight incline. Easy walking.

Moderately Steep

Up to a 45 degree angle.

Very Steep

Very steep. Will require using hands at times. Fall could lead to injury or even death.

Vertical

Straight up. "Rockclimbing." For safety, most people would "toprope," i.e. fasten an anchored rope to oneself attended by a belayer. Only experienced rock climbers would attempt climbing without rope.