Given series: 6, 20, 43, ?, 265

To find the missing term in the series, let's analyze the pattern and identify the relationship between the terms.

Pattern observation:
- The difference between the first and second terms is 20 - 6 = 14.
- The difference between the second and third terms is 43 - 20 = 23.
- The difference between the third and fourth terms is unknown.

Finding the pattern:
Let's examine the differences between consecutive terms to see if there is a consistent pattern.

- The difference between the first and second terms is 14.
- The difference between the second and third terms is 23.
- The difference between the third and fourth terms is unknown.

The differences between consecutive terms are not following a consistent pattern. Therefore, we need to look for another pattern in the series.

Finding an alternate pattern:
Let's try to find an alternate pattern by examining the ratios between consecutive terms.

- The ratio between the second and first terms is 20/6 = 3.33 (approx).
- The ratio between the third and second terms is 43/20 = 2.15 (approx).
- The ratio between the fourth and third terms is unknown.

The ratios between consecutive terms are also not following a consistent pattern. Hence, we need to explore another approach.

Using the square of the position number:
In some series, the pattern may depend on the position number of the term. Let's try squaring the position numbers and see if it helps in finding a pattern.

- The square of 1 is 1, which is not equal to the first term 6.
- The square of 2 is 4, which is not equal to the second term 20.
- The square of 3 is 9, which is not equal to the third term 43.
- The square of 4 is 16, which is equal to the missing fourth term.

Conclusion:
By squaring the position number, we obtain a term that matches the missing term in the series. Therefore, the missing term is 16.

Answer: The missing term in the series is 16.