pd.concat((train_data.iloc[:, 1:-1], test_data.iloc[:, 1:]))

This line of code is concatenating two dataframes:

- `train_data.iloc[:, 1:-1]`: This selects all rows and columns from the second column up until the second-to-last column from the `train_data` dataframe.

- `test_data.iloc[:, 1:]`: This selects all rows and all columns from the second column to the end of the `test_data` dataframe.

The `pd.concat()` function is used to concatenate these two dataframes along axis 0 (i.e., vertically) into a single dataframe. The resulting dataframe will contain all the rows from `train_data` and `test_data` except for the last column of `train_data` (which contains the target variable).