The definition, and why it is narrow
Plenty of things get called partnerships. A supplier contract is called a partnership in the press release. A discount is called a partnership on a slide. The word has been worn thin by use, which is a nuisance, because there is a real category underneath it and the real category has particular problems.
The narrow definition has three parts. First, the work is continuing rather than a single transaction: the parties expect to be dealing with each other again. Second, the work is coordinated rather than merely exchanged: each side changes what it does because of the other. Third, ownership does not move: neither party can instruct the other, and neither can be overruled.
That third condition is what makes alliances a distinct discipline. Inside one organisation, a disagreement between two departments has a resolution route: somebody senior enough decides. Between two organisations, there is no such person. Every mechanism an alliance uses to get decisions made is a substitute for an authority that does not exist.
What it is not
It is worth being precise about the neighbouring categories, because choosing the wrong one is expensive.
A purchase is not an alliance. If one party specifies what it wants, pays for it, and can replace the provider without changing its own plans, that is procurement. It may involve a long relationship and real goodwill, but the risk is not shared and the coordination is one-directional. Treating a supplier relationship as an alliance tends to produce a lot of joint meetings and no change in behaviour.
A merger or acquisition is not an alliance either, and it is the option that alliances are usually chosen instead of. Acquisition resolves the authority problem completely: after it, one party decides. It costs far more, takes far longer, and is very hard to reverse. Parties choose an alliance when they want some of the coordination benefit without paying that price, and they should be clear-eyed that they are accepting a weaker instrument in exchange.
A joint marketing gesture is not an alliance in the sense used here unless something in the operating routine of each party actually changes. A shared logo on a stand is a promotional act. It becomes an alliance when the two sales teams start planning around each other.
The alliance is the overlap
The most useful mental picture is two blocks with an overlap between them. The blocks are the parties, with their own owners, their own staff, their own priorities and their own separate reasons for existing. The overlap is the alliance: the specific area of activity that the parties have agreed to run jointly.
Nearly every practical question becomes clearer when it is asked about the overlap rather than about the relationship as a whole. What exactly is inside it? Who works in it? Whose budget pays for it? Who owns what gets made there? What happens to it if one party changes direction? A relationship described only as a partnership answers none of those. An overlap described precisely answers all of them.
The overlap is also the thing that should be small at the start. Arrangements that begin with a large declared scope and a small amount of real joint work tend to shrink to nothing. Arrangements that begin with a small, specific, genuinely shared piece of work tend to grow, because success in a narrow area gives both sides a reason to widen it.
Why organisations do it at all
There are only a few underlying motives, and it helps to know which one is operating.
Access: one party can reach buyers, markets or regions the other cannot, and building that reach from scratch would cost more than sharing the margin. Capability: one party can do something the other cannot, and learning it would take years. Capacity: one party has plant, people or infrastructure standing idle while the other has demand it cannot serve. Risk: the work is large or uncertain enough that neither party wants to carry all of it. Legitimacy: a joint effort carries standing that a single party's effort would not, which is why standards bodies and trade associations exist.
When both sides can state the same motive in the same words, the arrangement usually has a chance. When each side privately holds a different motive — one wants capacity, the other wants to learn the capability — the arrangement will still be signed, and it will fail later for reasons that look mysterious at the time.
Asymmetry is normal
Partnership language implies equality, and almost no partnership is equal. One side is usually larger, or holds the customer relationship, or owns the thing the other party needs. That is not a defect and it does not need to be denied. It does need to be acknowledged, because the terms that make sense between equals are not the terms that make sense across a large difference in size.
The smaller party's realistic concerns are dependence and displacement: what happens if this becomes most of our revenue, and what happens if the larger party decides to do this itself. The larger party's realistic concerns are consistency and control: whether the smaller party can deliver at the standard its own name implies. Good arrangements name both sets of concerns during the talks rather than discovering them afterwards.
Where this leads
Once the overlap is defined and the motive is stated, the next question is what shape the arrangement should take: a channel relationship, a joint venture, a consortium, or simple joint promotion. Those shapes differ mainly in how much control each party gives up and how hard the arrangement is to leave.