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If soil drains well, has ample water, is neither too acid nor too alkaline, yet still fails to sustain plant growth well, it may be deficient in nutrients - most likely nitrogen.

Any material originating from a living organism - peat moss, ground bark, compost or manure, for example - that can be dug into soil to improve its condition is referred to as organic matter.

A highly water-retentive, spongy organic soil amendment, peat moss is the partially decomposed remains of any of several mosses.  It is somewhat acid in reaction, adding to soil acidity.  Sphagnum peat moss is generally considered to be highest in quality.

A perennial is a non woody plant that lives for more than 2 years.  The word is frequently used to refer to a plant whose top growth  dies each winter and re-grows the next spring, but some perennials keep their leaves all year.

Perlite is a mineral expanded by heating to form very lightweight, porous white granules useful in container soil mixes to enhance moisture and air retention.

Using thumb and forefinger to nip off the tips of branches is called pinching back.   This basic pruning technique forces side growth, making the plant more compact and dense.  It is especially useful with annuals, house plants and shrubs.

A potting soil is a soil mix designed especially for plants growing in containers.  

In gardening usage, propagation refers to the many ways of starting new plants.   These methods range from planting seeds to the more complicated arts of budding and grafting.  With the exception of seed sowing, all methods of starting new plants are known as vegetative propagation: the new plants that result will be identical to the parent plant.

Pruning is both a skill and an art.  The skill is in making cuts that callus (form a thickened tissue that seals off wounds) properly and minimize the chance for decay.   The art is in making cuts in the right places so that the plant takes on a handsome form and is prolific if grown for flowers or fruit.