Stop&Go, what does this usually mean?

[AllIn3High]

Preflop is certainly debateable, but I figured he'd raise a lot of worse hands from the CO. But I pretty much regret it, as it gave me a tough river decission.

But I see these stop&go's on the river quite a lot and I wonder what they mean most often? Missed draw or a real hand making sure I don't check behind?

EDIT: Assuming an unknown.


Party Poker No-Limit Hold'em, $ BB (7 handed) pokerhand.org hand converter (http://www.pokerhand.org)

BB ($84.75)
UTG ($444.2)
MP1 ($204.7)
MP2 ($71.88)
CO ($260.55)
Hero ($196)
SB ($342.45)

Preflop: Hero is Button with Q/images/graemlins/spade.gif, K/images/graemlins/heart.gif. SB posts a blind of $1.
<font color="#666666">3 folds</font>, <font color="#CC3333">CO raises to $7</font>, Hero calls $7, <font color="#666666">2 folds</font>.

Flop: ($17) 5/images/graemlins/diamond.gif, Q/images/graemlins/diamond.gif, 9/images/graemlins/club.gif <font color="#0000FF">(2 players)</font>
<font color="#CC3333">CO bets $15</font>, Hero calls $15.

Turn: ($47) 9/images/graemlins/diamond.gif <font color="#0000FF">(2 players)</font>
CO checks, <font color="#CC3333">Hero bets $25</font>, CO calls $25.

River: ($97) 8/images/graemlins/spade.gif <font color="#0000FF">(2 players)</font>
<font color="#CC3333">CO bets $75</font>, Hero???