When you're invested in a business as large as Amazon (AMZN 0.83%), you must pay attention to all of its businesses. The company is best-known for its online retail operation, but there are opportunities among its other segments that could provide serious growth.

For example, Amazon's cloud computing segment, Amazon Web Services (AWS), has emerged as an essential growth and profit center for the overall company, but two segments that posted AWS-like growth last quarter were third-party seller services and advertising.

Amazon's second-largest segment

Third-party seller services isn't a new vertical -- it started appearing in financial reports as far back as four years ago. However, its growth resurgence is what makes me bullish.

In the third quarter, the segment grew its sales 18% year over year (23% on a currency-neutral basis). This is a strong uptick from the previous year of growth.

Revenue Growth (YOY)* Q3 2021 Q4 2021 Q1 2022 Q2 2022 Q3 2022
Third-party seller services 18% 12% 9% 13% 23%

Data source: Amazon. YOY = year over year. *Currency-neutral figures.

Third-party sellers account for the majority of Amazon's total paid units sold at 58% in the third quarter, its highest makeup ever.

That's a critical development for a company trying to keep regulators off its back. If Amazon can show it sells more of its clients' items than its own, it has a case that it's providing an important marketplace to small- and medium-sized sellers rather than stealing their business.

Although it wasn't mentioned in the latest earnings call, another area where Amazon could be seeing expansion is its Buy with Prime offering. This feature allows third-party websites to give their customers the ability to purchase an item using Amazon Prime checkout while also promising the same fast delivery Prime is known for.

The third-party seller services segment is Amazon's second largest with nearly $112 billion of revenue in the trailing-12-month period (or about 22% of the top line). Investors should keep an eye on this business in the fourth quarter, but if it can sustain growth at these levels, it will be a tremendous boost for the company.

Advertising growth even stronger than expected

Starting in the fourth quarter of 2021, Amazon broke out its advertising business from the "other" segment. Its growth has been nothing short of impressive.

Revenue Growth (YOY)* Q3 2021 Q4 2021 Q1 2022 Q2 2022 Q3 2022
Advertising services 52% 33% 25% 21% 30%

Data source: Amazon. YOY = year over year. *Currency-neutral figures.

Bear in mind nearly every other advertising-focused company, whether it's Alphabet or Meta Platforms, posted hardly any advertising revenue growth in their most recent quarters. Many companies are tightening up their ad budgets due to economic uncertainty. While Amazon may experience this weakness eventually, advertising services are going full-steam ahead, posting third-quarter revenue of $9.5 billion or just under half the size of AWS.

Advertising growth actually led all of Amazon's business units with the exception of the small "other" category (which includes licensing and distribution of video content, shipping services, and co-branded credit card agreements). This segment surged 163% year over year to $1.3 billion last quarter.

And that brings us back to why Amazon is a great investment: It's always innovating and finding new ways to expand its reach. This fact is why I'm an Amazon shareholder, and the latest results have only made me more confident.