Buy Side IB

Simply put buyside IB doesn't exits. (Unless you are talking about Buy-Side M&A, which I will cover last)

Those buy-side jobs that you are probably referring too are comprised of mainly Hedge Funds (HF) jobs, Private Equity (PE) Jobs, and Venture Capital (VC) jobs. I would say most exit to PE though with HF being second by a a big amount. (PE is considered the most desirable). Simply put what separate these jobs into Buy-Side is you actually have an investment and ownership in whatever company you are investing in. I'm going to talk about PE in this because that is what I know the best, still no professional only an intern so don't kill me in the comments.

Private Equity vs Investment Banking

(Buy-Side) Private Equity: a form of investment where they invest directly to purchase ownership in private companies, often with the goal of restructuring, improving their operations, and ultimately selling them for a profit in 5 - 7 years. (This is the usual sell or exit period) Unlike publicly traded companies and buying stocks, these investments are not traded on public stock exchanges, making them privately held and less accessible to the general public. Private equity firms typically seek to actively manage their portfolio companies to enhance their value and generate returns for their investors.

(Sell-Side) Investment Banking: it is comprised of a lot of different types of IB, I like to explain it usually in terms of a doctor in the sense that someone has different specialties or services like their are brain surgeons and heart surgeons which are 2 different jobs but still fall under the umbrella of "doctor/surgeon".  IB services often include underwriting securities, facilitating M&A (mergers and acquisitions), offering financial advisory services, and managing capital raising activities all of which are different teams and all are other concepts and types of jobs and daily tasks some task overlap though but will not define each one and sometimes banks do not even offer all of these services. 

Difference

Big difference is that PE does work to buy companies and IB work is advising companies. So basically Buy-Side has an actual stake in the company where as Sell-Side doesn't give a shit and after the deal is closed it is not their problem anymore.

Maybe What You're Talking About

Lastly what you might be talking about with the vague title isn't Buy-Side Jobs but Buy-Side M&A which is a type of deal you can do in IB. M&A is split up into 2 types which are Sell-Side M&A and Buy-Side M&A.

Sell-Side M&A: refers to the perspective of the party that is selling or divesting a company or its assets. In this scenario, the company or its owners hire investment bankers to help them find potential buyers, negotiate deals, and manage the overall sales process. This is the most common version of M&A because often times a company does not have time, manpower, or knowledge to find buyers. 

Buy-Side M&A: represents the perspective of the party looking to acquire another company or its assets. Companies seeking growth or diversification through acquisitions. The acquiring company or investor may hire investment bankers or advisors to help identify suitable target companies, conduct due diligence, negotiate terms, and facilitate the acquisition process. This is less common because often when a company wants to grow they already have an idea of what they are looking to get into or expand and what would fit in with their company's business model. But again what makes this not a "Buy-Side" Job like HF,PE, VC is the fact that the IB is purely just an advisory service and will have zero say in any of the companies operations after the deal is closed.

NGL this is also quite complicated to explain to a 4 year old with the amount of concepts and different jobs and types of IB there are. Also dif types of HF, PE, VC too but not getting into those.

Above comment is waaaay too long

Buy side IB: you are advising the buying agent ( someone who is looking to acquire a company). Usually a sponsor or strategic

Sell side IB: you are advising the selling agent ( someone who is looking to sell their company)