If you're attempting to understand Eliot's "The Waste Land," you have a great deal of work ahead of you. Far too much goes into understanding this poem than can be included in one answer to your question. The best way for you to begin an attempt to understand the poem is to study the enotes Study Guide. Here's what the Guide says about the poem's title:
The title refers to a myth from From Ritual to Romance,in which Weston describes a kingdom where the genitals of the king, known as the Fisher King, have been wounded in some way. This injury, which affects the king’s fertility, also mythically affects the kingdom itself. With its vital, regenerative power gone, the kingdom has dried up and turned into a waste land. In order for the land to be restored, a hero must complete several tasks, or trials. Weston notes that this ancient myth was the basis for various other quest stories from many cultures, including the Christian quest for the Holy Grail. Eliot says he drew heavily on this myth for his poem, and critics have noted that many of the poem’s references refer to this idea.
The waste land in the myth mentioned above, then, is reflected by the waste land of the poem.
The enotes Study Guide lists two major themes in the work: disillusionment and restoration, and has this to say about its place in literature:
The most important aspect of the work, and the one that informs all others, is the literary movement to which it belongs, modernism, which this work helped define. Modernism is the broad term used to describe post–World War I literature that employs techniques Eliot uses in The Waste Land. These techniques, and all the techniques associated with modernist literature, expressed a rebellion against traditional literature, which was noted by its distinct forms and rules.
The above then should help you with a little insight into the meaning of the title, the themes, and the poem's place in Modernism.