Rejuvenation

Could someone please explain rejuvenation in simpler terms, not wikipedia language!
I just did an AQA practise question, worth 15 marks, and failed at it because I dont understand it, and don't know any landforms, so could you please explain:
a.) What rejuvenation actually is
b.) What a knick point is
c.) What a river terrace is
d.) What entrenched and ingrown meanders are, and what the differenceis between them and a normal meander!
Jeez my teacher sucks

Rejuvenation means getting re-energised ie gaining energy. A river gains energy (kinectic) from gravity, imagine water running over a surface like a gently tilted table. Then increase the tilt of the table - it runs faster ie has more energy!
When a river meets the sea..it loses this energy/ fall and this is called base level (hence deposits the sediment).
If sea level suddenly drops (eg ice caps grow or land rises - tectonic uplift) the river has further to fall - runs faster, so 'rejuvenated'. If it moves faster - it erodes deeper/ more.
A knick point is a waterfall - the river is 'rejuvenated' and erodes faster at weak point/ rock.
A river terrace is old flood planes...the rejuvenated river erodes down in stages, as land rises or sealevel falls.
An entrenched meander is just a very deep (rejuvenated) meander due to long periods of erosion by a re-energised river keeping eroding downwards as sl falls/ land rises eg river wear at durham city or the Grand Canyon/ Colorado.

That's as simple as I can make it!

a) Rejuvenation is where the river gains energy as a result of a change in the base level of the river e.g. the sea level. This can be due to both isostatic or eustatic change. As a result the river tries to adapt its new long profile and try to re-establish a graded profile.

b) Knick point is where there is a sharp change in the gradient of the river where the previous long profile meets the new long profile. This is usually marked by a waterfall or rapids as the river has increased energy to erode vertically due to increased potential energy..

c)River terraces are basically previous floodplains that are left above the present-day flood plain as a result of the downward erosion due to river rejuvenation. The river that has eroded downward once again establishes a river floodplain hence leaving the previous floodplain above the present-day one like a "terrace". Think of it terraces in football stadiums.

d)Entrenched meanders and ingrown meanders are both meanders that have been cut into the floodplain due to the river's vertical erosion. Entrenched meanders are where vertical erosion is much greater than the lateral erosion of the meander so you get a symmetrical cross-section and a deep gorge-like valley is formed. Whereas ingrown meanders are where vertical erosion is less than lateral erosion of the meander so you get an asymmetrical cross-section as the meander's usually processes would erode the other bank more.

Sorry for bad grammar/ it might not make sense! I am very very tired lol :P