The situation where heavy government borrowing to finance a deficit pushes up interest rates and reduces the funds available for private investment, so public spending "crowds out" private spending.
The definition (government borrowing raising rates and squeezing private investment) and its link to large fiscal deficits are standard fiscal-policy facts.
Crowding out (public borrowing reduces private investment via higher interest rates) versus crowding in (public investment encourages more private investment); the effect is strongest when resources are fully employed.
Large government borrowing raises interest rates and squeezes private investment; the opposite is crowding in.