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The tidal force is the net difference in gravitational force between two portions of a massive object due to the presence of a nearby body. The tides of the Earth's oceans are explained by the presence of the Moon, the Moon acting as the nearby body, contributing (differently) to the net gravitational force on the portions of the ocean that are nearer versus further from the moon.
When gravitational force is described as between finite-sized objects as opposed to being treated as idealized (infinitesimally-small) point masses, the forces holding the individual objects intact are affected by a tidal force, i.e., the gravity of the other body. The ground beneath my feet, besides being held down by Earth's gravity, is pulled slightly upward when the Moon is overhead. The resulting tidal force tends to stretch the body, e.g., making the ocean rise a bit at the point toward the Moon and also rise at the opposite point on Earth, where the tidal force is smaller, given that location is more distant from the Moon. The same force-differences affect solid ground, but with a much smaller displacement.
If rotation or orbit causes the direction of such a tidal force to change over time, the (possibly slight) elasticity of a body allows work to be done changing its shape, dissipating energy through frictional heat (tidal heating), which can change the orbit and/or rotation of the bodies (labeled tidal acceleration, or in the cases when the acceleration is slowing, tidal deceleration or tidal braking). This is a minor source of heat within the Earth but significant for numerous solar system moons. Over time, the bodies can settle into a tidally-locked situation (tidal locking) where the bodies' rotation matches the orbit, i.e., the same face of the body always faces its orbiting partner. Such tidally-locked bodies include many solar system moons, including Earth's.
Tidal forces also affect galaxies (galactic tide refers to the effect of tidal force of one galaxy on another), gas clouds, and other astronomical objects.
Tidal equilibrium takes place when tidal forces bring bodies into an equilibrium state, e.g., when tidal forces no longer affect the kinematics, which can be the case with tidal locking. For some three-body systems, e.g., a star, its planet, and the planet's moon, an equilibrium state is never reached.
Within the strong-field gravity of a black hole, tidal forces are extreme, rising to the point where they destroy anything solid. Thus, while the Moon does very-slightly raise the ground I'm standing on, if the Moon were sufficiently massive, it would rip the Earth apart. Spaghettification is a term for the extreme stretching of objects along the line through the black hole's center of mass, the object's own gravity drawing itself together along planes perpendicular to the line. The spaghettification phenomenon pulls apart stars too near a supermassive black hole.