The West refers to the large region Middle-earth and includes the lands of Beleriand (up to the end of the First Age) Lindon, Eriador, Gondor, Rhovanion, and others, essentially all the lands west of Rhûn and Mordor. It is also used to describe the Free Peoples of Middle-earth like the Elves, Men, Dwarves, Hobbits and Ents particularly during the Third Age. West is normally 'the good' versus the bad from the East. (i.e. Sauron, Harad and Easterlings)
The Beleriand consisted of mostly plains and lowlands with scattered woodlands, dense forests, and grasslands. The lands of Hithlum, Mithrim, and Dor-lómin were plateaus consisting of short grasslands and scattered woodlands surrounded by mountains. Dorthonion was mostly a plateau surrounded by a mountain range in its south and consisted of moorlands and dense forests in its north. There were some hill lands such as the ones near the Blue Mountains and Himring.
The Beleriand’s climate varied in degrees. The West Beleriand consisted of cold winter, cool to mild summers in the northern part with cold, dry prevailing winds from the north, and warm, moist prevailing winds from the sea. The southern part consisted of mild winters, mild summers with warm, moist prevailing winds coming primarily from the sea. The East Beleriand consisted of severe, dry winters, short, cool summers with strong prevailing winds coming form the northern part near Morgoth’s domain. The southern part had mild winters, mild summers with warm, moist prevailing winds from the sea with the exception of the realms of Maedhros and Maglor between Dorthonion and the Blue Mountains, which had cold winters and mild summers due to there proximity to the north.
After the fall of the Beleriand, the West’s terrain from Lindon to Rhovanion and Gondor was mostly lowlands and plains consisting of mostly shrubs, shrubs thickets and scattered woodlands. Grasslands prevailed in Rohan, formerly Calenardhon and dense forests were in areas such as Fangorn and Mirkwood. Hill lands were mostly in mid-Eriador, next to Misty Mountains, the Wold in Rohan, and the lands east of the Grey Mountains.
The climate variation was mostly the same as it was during the First Age with severe winters and cool summers in the lands near the cold north, with cold prevailing winds. Cold but milder weather conditions dominated northern Eriador and northern Rhovanion, and south from that mild conditions with a tendency toward fog existed throughout most of the rest of Eriador and the lands to the south, with warm, moist prevailing winds coming from the sea. Southern Rhovanion was overall a bit colder then the north possibly due to its shielding from the warmer prevailing winds from the sea, from the Misty Mountains. Both Rohan and Gondor were warmer climates due to their proximity to the south and the influence of the warm prevailing winds from the sea.
During the Years of the Trees and the First Age during the days of the Beleriand, the West consisted of mostly good races which were Moriquendi elves, Noldorin exiles, and later Edain men with some faithful Easterlings, and Dwarves living in the mountains. The enemy was in the North. With the destruction of the Beleriend, the West became the lands of Lindon, Eriador, Gondor, Rhovanion, and others with the East being the lands of Rhûn and Mordor. In the Second Age, the West's population was mostly primitive men and a few elves located mostly in Lindon, Eregion, and some in Greenwood the Great. There were some tribes of Orcs living in the Misty Mountains with some in the Grey Mountains. The enemies, Sauron and Easterlings mostly came from Mordor and Rhûn in the East until their defeat during the War of the Last Alliance.
In the Third Age, the West was mostly nations of Men living in the Realms in Exile (Arnor and Gondor). Other races such as Dwarves and Elves decreased in numbers becoming hidden peoples living in realms such as: Moria, the Lonely Mountain, Lothlórien, and Mirkwood. Hobbits, once a minor race living in the Gladden Fields migrated to Bree and then The Shire, the most populated of their realms. Ents diminished in numbers remained solely in Fangorn forest. The enemies from then on were traditionally located in the East, though for some time many of the threats came from within the West in places such as Angmar, Misty Mountains, and Dol Guldur but during the latter half of the age the enemies were solely from the East.