I see a skin bump on the left leg of my husband. what might be the reason? m sure it's not pimple since its big.

Boil is: probably what it is . Abcess is also a possibility.

Also consider Lipoma: If it is red, sore, and increasing in size over time- Dr Yetimyan is absolutely right. A boil or abscess will generally worsen until it is drained. If it has no color change, and is not painful, it could be a lipoma. Purple bluish lumps can be lymphangiomas. These last two are not concerning.. There are a few other things to consider, but it would depend on it's characteristics.