Landscape

A knoll is a small hill.

A lake is a very large amount of water, usually in a valley in the mountains. Some lakes form in a crater where a meteor has hit. Most lakes are fresh water, some lakes near the sea may be salt water. A very very small lake in a park or a backyard is called a pond.

Mangroves are a kind of tree that grow along with other plants as mangals. Mangroves grow in the area where the tide flows through them, so they spend some of their time under water and some of their time dry. Many sea creatures live among the mangroves's roots, and mangroves are particularly important as a safe place for baby sea creatures when they are still very young.

A moor is an area of land with poor drainage, usually overgrown with heather and covered in a thick layer of peat.

Mountains are very big hills, and are usually steep and rocky. Some mountains are so high they have snow on the top.

The ocean is the vast expanse of salty water that covers most of the Earth.
Another word for ocean is sea.

A plain, also called a savanna, field, grasslands or prairie, is a large open expanse that is covered mostly with grass, and very few trees. Grasslands are found in drier regions all over the world.

A pond is a small body of water, smaller than a lake but bigger than a puddle. Ponds are often man-made and are put into gardens as a decorative feature.

Puddles are small pools of water on the ground. Puddles are left in small dents in the ground after it rains, or when water has been spilled on the ground.

Rainbows happen when the sun shines through a very fine spray of water, like rain in the air or the spray from a garden hose or even from a waterfall.
The rainbow is colourful because as sunlight travels through the water spray, it splits into a spectrum of colours. All the colours you see in a rainbow are there all the time in normal light, but they are mixed up together so you only see white light.
You can also see the colours of the rainbow by shining light through a prism.