In Spain, the "participaciones" of limited liability companies literally represent the quota of capital subscribed or acquired by a partner, and cannot be traded as an asset with its own independent value.

I have seen other terms used in English, but I believe "quota" is the one that most adequately conveys the idea that a "participación" is just that, a portion of the capital allocated to a partner, and not stock.

ociedades de Responsabilidad Limitada (“S.L.”)
1) Minimum capital stock: 3,006 Eur., which must be fully paid in.
2) Greater flexibility than an S.A.; intended to be used by more closely held entities.
3) Company interests not so freely transferrable as with an S.A.
4) Capital stock must be divided into participation units, but these need not all be the same (i.e. different voting rights allowed).

also Deloitte:
The minimum capital for a S.L. is €3,000. All share capital (and share premium) must be fully paid in upon formation. A S.L.´s capital is
divided into participations (participaciones sociales). Participations are not marketable securities and cannot be represented by means
book entries or share certificates.