Investment property is primarily purchased with the intent of eventually making a profit from its sale. Typical examples include stocks, bonds, collectibles, and land.
Generally, you don't use investment property in your day-to-day living like you do personal-use property.
Personal-use property is not purchased with the primary intent of making a profit, nor do you use it for business or rental purposes. It includes things like your home, furniture, appliances, personal vehicle, and clothing
Example: You bought a cabin so you could get away on weekends. Although you certainly wouldn't mind making a few bucks when it comes time to sell, your primary motivation for the purchase was to have some family fun and relaxation. This would make your vacation cabin personal-use property rather than investment property.
On the other hand, if you purchased the cabin in a remote up-and-coming vacation hotspot and plan to sell it for a profit when the time is right, it would be investment property.
Why does it matter? Although you're supposed to report profits (capital gains) from the sale of both investment and personal-use property, you can only deduct losses from the sale of investment property.