In short: This glossary explains the main terms used in tail spend management, from spot buys and C-suppliers to single creditor, P2P and Peppol. Each definition is written to be short and practical.
Tail spend and suppliers
Tail spend
The large number of small, non-strategic purchases outside your main contracts. It typically accounts for most suppliers and invoices, but a small share of total spend.
Spot buy
A one-off purchase of a product or service that is not covered by an existing contract or catalogue.
C-supplier
A supplier with low spend and low strategic importance, often used once or a few times a year. Together, C-suppliers make up the long tail of the supplier base.
Single creditor
One partner that pays all tail suppliers and invoices your company. Your ERP holds one creditor instead of hundreds of small ones.
Single vendor
One supplier that handles all purchases in a category or in the whole tail, including sourcing and ordering from other suppliers.
Supplier consolidation
Reducing the number of active suppliers in your ERP, for example by moving tail suppliers to a single creditor.
Supply base reduction
Another term for supplier consolidation: fewer suppliers to onboard, check, pay and manage.
Maverick spend
Purchases made outside the agreed procurement process, contracts or approved suppliers.
One-time vendor
A supplier you buy from once or very rarely. Creating a full vendor record for such a supplier often costs more than the purchase itself.
Vendor onboarding
Creating and checking a new supplier in your systems: company data, bank details, VAT number and compliance checks.
Process and systems
Procurement outsourcing
Handing over (part of) the purchasing process to an external partner, such as sourcing, ordering, invoicing and payment of tail spend.
Purchase-to-pay (P2P)
The full process from purchase request and approval to order, delivery, invoice and payment.
Purchase order (PO)
The document that confirms an order to a supplier. With a single creditor, every invoice refers to one PO.
Three-way match
Checking that the purchase order, the delivery and the invoice correspond before payment.
Invoicing and data
Peppol
The European network for exchanging structured e-invoices and other business documents. In Belgium it is the main network for mandatory B2B e-invoicing since 2026.
E-invoicing
Sending invoices in a structured electronic format that software can process automatically. A PDF is not a structured e-invoice.
Supplier enablement
Getting suppliers ready to work with your processes and systems, for example to receive orders and send e-invoices.
Sourcing
Finding and selecting suppliers for a need, often through a request for quotation (RFQ).
RFQ (request for quotation)
A request to several suppliers for a price offer on a specific product or service.
Catalogue (punch-out)
A list of products with agreed prices that employees can order from, sometimes opened directly from your own procurement system.
Spend visibility
Insight into what is bought, from whom, by whom and at what price, across all suppliers and cost centres.
Accounts payable (AP)
The finance team or process that receives, checks and pays supplier invoices.
Want to know how these concepts apply to your organisation? Read how a single creditor model cuts AP costs, see the FAQ or contact us.
