Deloitte managed a semi-intelligible explanation. It's called "super" when an income tax deduction is applied twice for the same item (e.g. for R&D)...
In early 2015, Slovakia introduced a new type of tax incentive aimed at supporting companies conducting corporate R&D (most common is development of new or substantially improved products, services, technologies and processes). [...] Similar regimes have been in use for years in the world's most advanced economies.
In practice, eligible expenses can be deducted from the tax base twice. First as a normal tax-deductible expense and second as an additional super-deduction. [...]
Super-deductions can be utilized by any company, which in the relevant tax period incurs expenses directly related to R&D projects. In case of tax losses, the super-deduction may be transferred to the next tax period (up to maximum of four subsequent years).
KPMG has a more concise definition and some examples/figures:
Income tax is reduced by deducting
R&D expenses from the tax assessment basis by
more than 100% (“super deduction”) or from the
tax liability (“tax credit”). [...]
Tax-free amounts are applied to obtain a discount
of more than 100% of the qualifying R&D costs.
From a practical perspective, this is usually
achieved by deducting these costs against tax
more than once. The majority of multipliers in
other jurisdictions are between 130% and 210%.
This leads to the fact that these increased R&D
expenses can be also claimed as expenses
for tax purposes and reduce the taxable profit