To determine how much meat the caterer needs to order for 100 guests, we start by establishing the relationship between the number of guests and the amount of meat needed.
Given the caterer needs 40 pounds of meat for 25 guests, we can find the amount of meat needed per guest:
\[ \text{Meat per guest} = \frac{40 \text{ pounds}}{25 \text{ guests}} = 1.6 \text{ pounds per guest} \]
For 100 guests, we multiply the amount of meat needed per guest by the number of guests:
\[ \text{Amount of meat for 100 guests} = 1.6 \text{ pounds per guest} \times 100 \text{ guests} = 160 \text{ pounds} \]
Therefore, the caterer should order 160 pounds of meat for 100 guests.
The answer is 160 pounds.