The sunlight coming from the west in the late afternoon; the setting/afternoon sun (often strong and hot when it enters rooms).
夏は西日が強くて、午後は部屋が暑くなる。
In summer the westering sun is strong, and the room gets hot in the afternoon.
窓に西日が差し込んで、テレビが見にくい。
The afternoon sun is shining through the window, making it hard to see the TV.
ベランダの洗濯物は西日に当たると色あせやすい。
Laundry on the balcony fades easily when exposed to the afternoon sun.