Spanish term (edited): [dos] anualidades de ejecución periódica

I'm fairly sure the meaning here is that the contract is to be performed over two years, although these will be split into (and paid in) two periods because the (government?) budget is perhaps only approved on a year-by-year basis. It relates to the concept of the "contrato de ejecución periódica" or "de tracto sucesivo", and it could mean that the contract sets specific milestones to be delivered in a certain period but that it is awarded for the whole period. The "ejecución" here refers to performance, not payment.

Contrato de ejecución periódica.- Son los contratos que se agotan en un determinado lapso, en ellos el tiempo es un factor fundamental.
http://www.contrato.pe/2016/01/clasificacion-de-los-contrato...

Continuing contract is a contract calling for periodic performances. Under such a contract, performance is in several units over a period of time. It is an executory, as distinguished from an executed contract.

The following is an example of a state law (Florida) defining the term:

According to Fla. Stat. § 443.091, "Continuing contract" means a written agreement that is automatically renewed until terminated by one of the parties to the contract.
http://definitions.uslegal.com/c/continuing-contract/

Continuing Performance Contracts

Continuing performance contracts are characterized by a legal relationship in which the parties have committed themselves to deliver one or several goods or services to each other over a definite or indefinite period of time. That performance should be continuing, recurrent or successive. Examples of continuing performance contracts are distribution agreements, employment agreements and leases or tenancy agreements.
http://www.burenlegal.com/en/nieuws/2013/10/04/alert-termina...


There are some interesting comments and answers here, but I think the answer chosen was the correct one.
http://www.proz.com/kudoz/spanish_to_english/law_contracts/1...